Mechanical     Drafting 


REVISED  IN  1915 

By 

THE  DEPARTMENT  OF  GENERAL  ENGINEERING  DRAWING 

H.  W.  MILLER,  M.E. 

•*.   K.  STEWARD,  C.E.  F.  M.  PORTER,  M.S. 

H.  H.  JORDAN,  B.S.  H.  O.  RUGG,  C.E. 

R.  CRANE,  S.B.  C.  A.  ATWELL,  B.S. 

In  the  University  of  Illinois 
Urbana,  Illinois 


(Original  edition  by  H.  W.  MILLER) 


The    Manual    Arts    Press 
Peoria.    Illinois 


Copyright,  1912 
H.  W.  Miller  and  R.  K.  Steward 
Copyright.  Revised  Edition,  1916 

H.  W.  Miller 
Third  Edition,  1917 


PRE 


LIBRARY 

STATE  NORMAL  SCHOOL 

MANUAL  ARTS  *NO  HOME  ECONOMICS 

SANTA  BARBARA,  CALIFORNIA 

ACE      !«»*_ 


In  writing  the  original  edition  of  this  text  it  seemed 
wise  to  the  author  to  base  its  arrangement  and  content 
upon  two  principles  which  considerable  experience 
proved  sound.  These  principles  are :  first,  that  the  stu- 
dent can  just  as  well  and  perhaps  better,  be  taught  the 
use  of  instruments  on  work  that  will  at  the  same  time 
haVe  educational  value;  second,  that  for  greatest  effi- 
ciency in  teaching  drawing  the  text  should  be  made  so 
complete  and  follow  the  class  room  work  so  closely  that 
lecturing  is  unnecessary. 

The  above  principles  were  followed  by  first  design- 
ing a  very  flexible  course  in  drafting,  substituting  draw- 
ings of  machine  parts  for  the  conventional  geometrical 
figures.  The  work  was  arranged  into  definite  groups, 
according  to  subject,  each  group  being  scheduled  for  a 
definite  amount  of  time.  Second,  the  text  was  so  ar- 
ranged that  section,  lesson  or  chapter  one,  gave  all 
information  necessary  for  the  work  included  in  group 
one,  etc. 

After  three  years '  very  satisfactory  trial  of  the  text, 
^  the  department  of  drawing  has  undertaken  a  complete 
09  revision  with  the  desire  that  the  work  shall  be  not  only 
CT>  a  text,  more  complete  than  the  first,  but  also  a  book  of 
reference  that  will  be  of  service  after  the  student  has 

"^completed  the  course.  TT    TTT    n-r 

o  H.  W.  MILLER. 

2   October,  1915. 


CONTENTS 

PAGE 

Chapter  1.     Lettering,  Freehand  and  Mechanical 7 

Chapter  2.     Use  of  Instruments 29 

Chapter  3.     Orthographic  Projection  52 

Chapter  4.     Working  Drawings  65 

Chapter  5.     Fasteners,  Threads,  Bolts  and  Nuts,  etc 88 

Chapter  6.     Shop  Terms,  Tools,  Machines,  etc 106 

Chapter  7.     Isometric  and  Oblique  Projection 125 

Chapter  8.     Machine  Sketching 147 

Chapter  9.     Perspective     151 

Appendix     161 


MECHANICAL   DRAFTING 

CHAPTER  1 

LETTERING 
FREEHAND 

(1)  Freehand  or  offhand  lettering  is  so  much  a  part 
of  every  engineer's  daily  routine  that  to  be  unable  to 
letter  with  speed  and  grace  is  considered  an  inexcusable 
discredit.  The  results  of  practice  show  that  no  one  need 
be  embarrassed  long  because  of  the  lack  of  this  skill,  for 
anyone  can  learn  to  letter.  However,  the  acquisition  of 
proficiency  demands  what  skill  in  any  manual  perform- 
ance requires, — more  or  less  experience  and  careful  study 
of  principles. 

It  is  fortunate  for  the  beginner  in  lettering  that  there 
are  very  few  elements  that  must  be  mastered.  Most 
engineers  use  extremely  simplified  styles  of  freehand 
letters.  The  Reinhardt  alphabet  (slant  or  vertical)  is 
especially  noted  for  its  simplicity  as  it  has  been  stripped 
of  all  superfluous  appendages. that  made  formed  styles 
both  complicated  and  time-consuming  in  their  use.  In 
the  practice  of  either  type  the  beginner  will  find  that  all 
of  the  letters  are  made  up  of  but  two  or  three  charac- 
teristic elements  or  strokes,  each  of  which  is  easily 
constructed. 

The  first  style  or  type  presented  is  the  Reinhardt 
slant.  It  should  be  mastered  thoroly  because  it  is  in  use 
in  most  drafting  rooms  and  colleges.  It  is  probable  that 
its  use  in  over  eighty  per  cent  of  the  large  drafting  rooms 


MECHANICAL  DRAFTING. 

of  the  country  is  due  to   its  legibility  and  ease  and 
rapidity  of  construction. 

EQUIPMENT 

(2)  Selection  of  Lettering  Pens.  For  a  pure  type  of 
either  Eeinhardt  or  vertical  letter,  such  a  pen  should  be 
used  as  will  give  a  stroke  of  uniform  width,  weight,  or 
heaviness,  when  it  is  moved  up,  down,  right,  left,  or  diag- 
onally on  the  paper;  otherwise  the  letter  will  have  a 
shading,  which  does  not  belong  to  the  types  mentioned. 


Fig.  1 


Some  pens  which  have  proven  satisfactory  for  letters 
of  a  uniform  weight  are  the  Sheppard  lettering  pen, 
Paysant  pen,  Moore's  Non-Leaking  fountain  pen,  and 
any  of  the  steel  points  known  as  ball  pointed  pens. 

Inking  of  Pens.  Apparently  a  great  part  of  the 
trouble  experienced  in  the  use  of  the  above  pens  is  due 
to  improper  inking.  No  lettering  pen  should  ever  be 
dipped  into  the  ink  bottle.  The  proper  method  is  to 
transfer  by  means  of  the  quill  attached  to  the  cork  a 
small  amount  of  ink  to  the  inside  of  the  ball  pointed  pen 
or  between  the  nibs  of  the  Sheppard  or  Paysant  pens. 


LETTERING.  9 

It  is  well  to  hold  the  pen  point  over  the  bottle  so  that  any 
superfluous  ink  may  not  be  spilled  on  the  drawing  or 
desk.  The  word  of  warning  that  must  be  heeded  is  to 
use  only  enough  ink  and  no  more.  One  may  be  sure  of 
not  having  too  much  ink  on  the  ball  pointed  pen  if  he 
will  always  stroke  off  the  pen  upon  the  quill  before 
trying  any  letters. 

Slope  Guide.  Immediately  on  beginning  practice  on 
inclmed  freehand  letters  it  will  be  well  to  provide  oneself 
with  a  sheet  of  heavy  drawing  paper,  about  three  by 
eight  inches,  across  which  have  been  ruled  a  series  of 
heavy  parallel  lines  at  from  70°  to  75°  to  the  long  edge 
as  shown  in  Fig.  1.  These  lines  should  be  at  equal  inter- 
vals and  from  one-eighth  to  one-quarter  inch 
apart.  An  angle  of  approximately  72°  may 
easily  be  constructed  by  laying  off  a  right 
triangle  whose  base  is  2  and  altitude  6,  Fig.  2. 
If  this  sheet,  which  may  be  termed  a  slope 
guide,  be  laid  just  below  the  line  on  which 
the  freehand  letters  are  to  be  made,  it  will 
not  be  difficult  to  make  all  first  element 
strokes  parallel  to  each  other.  It  is  likewise 
well  to  make  use  of  such  a  guide  continually 
until  this  slope  has  become  perfectly  natural,  for  nothing 
so  detracts  from  the  good  appearance  of  inclined  letters 
as  a  difference  in  slope  of  the  stems. 

Paper.  A  good  quality  of  ledger  paper  will  be  found 
best  for  lettering,  inasmuch  as  it  has  a  smooth,  hard 
surface  that  takes  ink  evenly.  It  is  likewise  well  to  adopt 
a  standard  letter  size  sheet,  8y2xll,  which  will  be  found 
in  stock  in  any  printing  office  or  stationery  store,  and  to 


10  MECHANICAL  DRAFTING. 

which  all  modern  office  files  are  adapted  in  case  one 
wishes  to  file  the  finished  work. 

PRACTICE  ON  ELEMENTS 

(3)  Guide  Lines.  Unless  especially  printed  practice 
sheets  have  been  prepared,  the  beginner  should  rule  on 
the  blank  sheet  a  series  of  six  light  parallel  pencil  lines 
(preferably  parallel  to  the  short  edge  of  the  sheet)  at 
intervals  of  one  inch  and  six  at  intervals  of  one-half 
inch. 


Element  Number  I. 


nannnn 

Element  Number  £. 

Fig.  3 

First  element,  Stems.  Element  one  is  simply  a 
straight  line  of  varying  length,  Fig.  3,  and  making  an 
angle  with  the  vertical  equal  to  the  slope  adopted  for 
the  inclined  alphabet.  In  practice  this  slope  can  easily 
be  secured  by  placing  the  slope  guide  just  beneath  the 
guide  line  on  which  one  is  working.  Several  lines  of 
stems  should  be  made  on  the  practice  sheet,  using  the 
half  -inch  guide  lines,  each  with  a  single  downward  stroke 
of  the  pen  and  at  equal  intervals.  When  finished  the 
stems  should  all  have  the  same  slope,  be  evenly  spaced 
and  each  have  the  same  weight  or  thickness  thruout  its 
length  and  all  stems  of  the  same  weight. 


LETTERING.  11 

Second  element,  Ovals.  The  second  element  is  a  per- 
fect ellipse,  inscribed  in  a  parallelogram,  two  of  whose 
sides  are  parallel  to  element  one  and  whose  base  is,  for 
normal  letters,  a  little  less  than  the  vertical  height,  Fig.  3. 
This  element  can  be  made  with  one  stroke  of  the  pen, 
after  some  little  practice;  however,  it  is  advisable  for 
the  beginner  to  form  it  ill 
with  two  strokes,  as  shown 
in  Fig.  4,  making  slightly  r_^_^_^_^ 
more  than  half  each  time  l  7  7  J~  / 
and  letting  the  ends  of  the  Fis-  4 

strokes  overlap.     This  will  in  general  insure  a  better 
joint,  as  the  overlapping  tends  to  smooth  out  the  juncture. 


Fig.  5 

In  order  that  one  may  learn  the  shape  of  element 
number  two  in  the  least  possible  time,  it  is  suggested 
that  a  beginning  be  made  as  shown  in  Fig.  5,  with  the 
height  of  the  character  one  inch.  Using  the  one-inch 
spaced  guide  lines  already  on  the  practice  sheet,  rule  a 
series  of  parallelograms,  bases  one  inch  and  sides 
inclined  at  the  slope  angle.  Then  sketch  in  long  sweeping 
arcs  tangent  to  the  inclined  sides  at  their  middle  points, 
a,  Fig.  5 ;  next  follow  the  arcs  tangent  to  the  horizontal 
sides,  b,  Fig.  5.  The  completed  shape  now  suggests  itself, 
c,  Fig.  5,  and  a  few  smoothing  up  strokes  will  complete 
the  ellipse,  d,  Fig.  5.  It  should  be  remembered  that  the 


12  MECHANICAL  DRAFTING. 

ellipse  is  tangent  to  the  sides  of  the  parallelogram  at 
their  middle  points;  this  gives  the  necessary  tip  that  is 
essential  to  a  graceful  appearance  of  the  alphabet. 


'(a)         fr)      '  J  fcj  6/          ' 

Compressed  Normal  Extended. 

Fig.   6 

An  excellent  variation  of  this  exercise  is  that  of 
making  ellipses  of  varying  widths.  It  is  evident,  Fig.  6, 
that  this  process  will  yield  alphabets  of  widely  differing 
general  effect,  altho  the  elements  entering  into  their 
construction  are  identical.  The  types  of  letters  produced 
by  the  varying  widths  are  as  indicated,  compressed,  nor- 
mal, and  extended. 

The  sketch  exercise  just  outlined  should  be  repeated 
with  diminishing  heights  of  three-fourths,  one-half,  one- 
fourth,  and  finally  one-eighth  of  an  inch,  the  size  ordi- 
narily used  in  drafting. 

oadqbpcey 


Fig.  7 


FORMATION  OF  LETTERS 

(4)  In  Fig.  7  it  is  seen  that  the  lower  case  letters 
o,  a,  d,  q,  b,  p,  c,  e,  and  y,  and  capitals  C,  G,  0,  Q,  Fig.  10, 
are  simple  elements  or  combinations  of  elements  one  and 


LETTERING.  13 

two.    Element  one  and  a  portion  of  element  two  make 
up  lower  case  letters  g,  y,  j,  f ,  n,  h,  m,  r,  s,  and  u,  Fig.  8,  and 


X  S      I         J 

Fig.  8 


capitals  B,  D,  J,  P,  R,  S,  and  U,  Fig.  10.  The  remaining 
straight  stroke  letters,  i,  k,  1,  t,  v,  w,  x,  and  z,  Fig.  9,  and 
A,  E,  F,  H,  I,  K,  L,  M,  N,  T,  V,  W,  X,  Y,  and  Z,  Fig.  10, 

iklTvwxz 


Pig.  9 


are  perhaps  easiest  to  construct.  It  should  be  noted  that 
the  lower  case  letters  a,  c,  e,  etc.,  are  two-thirds  the  height 
of  the  capitals.  The  letter  t  is  five-sixths  height  and 

abcdefghijklmnopqrstu 
12.345  vwxyyz  6739O 

ABCDEFG  H IJ KLM N 
OPQFISTUVWXYZ 

Fig.   10 

b,  d,  h,  etc.,  are  full  height.  The  tails  of  the  letters  g, 
j,  p,  q,  etc.,  extend  below  the  base  line  one-third  their 
height.  Numerals  are  the  full  stem  height  except  when 
used  in  fractions  when  they  should  be  shortened  slightly. 
See  Fig.  10  for  complete  slant  alphabet  and  numerals. 


14  MECHANICAL  DRAFTING. 

VERTICAL  LETTERS 

(5)  In  Fig.  11  is  given  an  alphabet  of  vertical  let- 
ters.   The  principles  of  construction  are  of  course  iden- 
tical with  those  of  inclined  letters.     Practice   should 
begin  on  the  two  elements,  stems  and  ovals,  as  directed 
in  Art.  3.     No  vertical  guide  will  be  necessary  in  this 

abcdefghijklmnopqrstu 

12345  vwxyz   6789 

ABCDEFGHIJKLMN 

OPQRSTUVWXYZ& 

Fig.  11 

case,  inasmuch  as  everyone  has  a  well  developed  sense  of 
appreciation  of  the  vertical.  It  may  be  well  to  mention 
that  when  using  vertical  letters,  an  extended  style,  similar 
to  c  or  d,  Fig.  6,  is  always  easiest  of  execution  and  has  an 
excellent  appearance. 

MECHANICAL  LETTERS 

(6)  The  need  for  letters  made  entirely  with  instru- 
ments will  be  only  occasional,  and  space  will  be  given 
here  for  only  the  general  methods  for  laying  out  such 
work.    In  the  appendix  will  be  found  alphabets  of  vari- 
ous styles  for  use  in  the  construction  of  titles,  signs, 
name   plates,   etc.     These   may  be   constructed    either 
mechanically  or  freehand,  as  desired. 


LETTERING. 


15 


Unit  Space.  If  any  given  height  which  may  be 
assigned  to  a  letter  be  divided  into  six  equal  parts  (for 
methods  see  Fig.  12)  each  of  these  parts  is  termed  a 


\         \   chosen  distance 


\        \ 


A       1        2        3        45 

Fig.   12 


unit  space.  It  will  be  noticed  in  Fig.  13,  which  is  of  the 
mechanical  vertical  Gothic  alphabet  most  commonly  used 
by  engineers,  that  all  stems  are  of  equal  width,  that  is, 


16 


MECHANICAL  DRAFTING. 


LETTERING. 


17 


one  unit.  Either  an  extended  or  compressed  style  of 
letter  may  be  obtained  by  arbitrarily  increasing  or 
decreasing  the  unit. 

CONSTRUCTION  OF  LETTERS 

(7)  In  constructing  a  word  or  series  of  words,  the 
rectangles  which  will  enclose  the  individual  letters  can 
be  laid  out  most  rapidly  by  the  method  shown  in  Fig.  14. 
The  vertical  distance  at  the  left  extremity  of  the  line  is 


Fig.   14 

first  divided  into  six  units.  Any  desired  number  of  units, 
e.  g.,  5  for  the  letter  H,  may  then  be  carried  any  distance 
to  the  right,  by  means  of  the  T-square,  to  the  left  side 
of  the  H  rectangle,  and  then  by  means  of  the  45°  triangle 
to  the  upper  guide  line,  thereby  obtaining  the  location 
of  the  right  side  of  the  rectangle.  The  unit  width  of 
letter  stems  and  other  necessary  construction  may  also 
be  secured  thru  the  proper  use  of  the  45°  triangle  as 
shown  in  Fig.  14. 

For  letters  involving  arcs  of  circles,  after  the  enclos- 
ing rectangles  have  been  drawn,  the  centers  may  easily 
be  located  as  shown  in  Fig.  14  and  as  indicated  for  other 
similar  letters  in  the  Gothic  alphabet,  Fig.  13. 

In  the  construction  of  the  letters  B,  E,  F,  H,  R,  and 
S,  it  should  be  noted  that  the  intermediate  horizontal 
stroke  is  slightly  above  the  center;  for  A,  G,  and  P  it 


is 


MECHANICAL  DRAFTING. 


is  below.  The  letters  B,  E,  R,  S,  X,  and  Z,  and  the  nu- 
merals 2,  3,  5,  6,  8,  and  9,  Fig.  15,  will  have  a  more  pleas- 
ing appearance  if  the  width  of  the  top  section  is  less 
than  that  of  the  bottom. 


The  distance  d 


Fig.   15 


SPACING 


(8)  Having  learned  the  correct  shapes  of  the  indi- 
vidual letters,  it  becomes  necessary  to  direct  particular 
attention  to  their  combination  into  words  and  sentences 


LETTERING.  19 

in  headings,  signatures,  titles,  name  plates,  etc.  While 
it  may  be  aptly  said  that  beautifully  formed  letters  can 
result  only  by  a  process  of  designing  each  stroke  as  it  is 
executed,  this  is  more  especially  true  of  the  completed 
title  page  or  other  group  of  letters,  taken  as  a  whole, 
where  as  much  judgment  is  employed  in  the  determi- 
nation of  the  areas  to  be  left  white  as  those  to  be  made 
black. 

Methods  of  Areas.  As  a  help  in  securing  good  spacing 
by  eye  alone,  a  rule  that  has  proven  very  good  is  that  of 
making  the  total  areas  between  successive  letters  appear 
equal.  It  is  well  to  adopt  a  specific  area  for  this  unit. 
The  best  unit  area  is  about  one-third  of  the  area  of  the 
letter  M;  this  is  equivalent  to  a  linear  spacing  of  2  units. 

KEY  TO   TABLE,   PICK   16. 

To  obtain  the  space,  in  units,  to  be  allowed  between  any 
letter,  e.  g.,  A,  and  any  letter  of  the  alphabet  which  may 
follow  it  in  a  word,  it  is  seen  in  the  table,  Fig.  16,  that 
between  A  and  BDEF,  etc.,  one  unit  space  should  be  left 
and  between  A  and  CGO,  etc.,  one  half  unit.  In  every 
case  the  spacing  given  is  that  to  be  allowed  between  the 
letter  given  in  the  first  column  and  any  letter  of  the 
alphabet  which  may  follow  it  in  a  word. 


20 


MECHANICAL  DRAFTING. 


2 

1% 

1V4 

1V4 

% 

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tt 

Neg. 

A 

Ki^'R 

D 

CGOQSZ 

AX 

JTW 

VY 

B 

BDEFHI 
KLMNPR 

CGOQSC 

2 

X 

AJTWT 

\ 

C 

BDEFHI 
KLMNPff 

COOQSC 

Z 

X 

AJTWT 

V 

D 

BDEFH1 
KLMNPR 

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KLMNPR 

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KLMNPR 

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KLMNPR 

C 

COOQSZ 

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AJTWV 

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KLMNPR 

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AJTWT 

V 

K 

BDEFHI 
KLMNPrf 

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COOQSZ 

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AJTWT 

V 

I, 

BDEFHI 
KLMNPR 

C 

ACOOQS 

J 

TVWT 

M 

BDEFHJ 
KLMNPR 

t 

COOQSZ 

X 

AJTWT 

V 

N 

BDEFHI 
KLMNPR 

D 

COOQSZ 

X 

A.ITWT 

V 

0 

BDEFHJ 
KLMNPR 

COOQSD 

Z 

X 

AJTWT 

V 

I' 

BDEFHI 
KLMNPR 

U 

COOQSZ 

TVWXT 

AJ 

q 

ItliKKIII 
KLMNPR 

COOQRli 

Z 

X 

AJTWT 

V 

R 

BDEFHI 
KLMNPR 

COOQSU 

2 

X 

AJTWT 

V 

S 

BDEFHT 
KLMTfPR 

COOQSU 

2 

X 

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V 

T 

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KLMNPR 

D 

COOQSZ 

TVWXT 

A 

J 

U 

BDEFH1 
KLMNPR 

I) 

COOQS* 

X 

AJTWY 

V 

V 

BDEFHI 
KLMNPR 

0 

COOQST 
VWXYZ 

AJ 

w 

RDEFHI 
KLMNPR 

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A 

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X 

BDEFHI 
KLMNPR 

0 

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X 

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T 

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C 

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TV  W  X  V 

AJ 

7, 

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KLMNPR 

r 

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X 

ATVWT 

J 

Fig.  16 


LETTERING. 


Special  Cases.  The  method  of  areas  just  suggested 
can  be  easily  applied  in  spacing  the  complete  rectangular 
letters,  H,  M,  etc.;  and  after  some  practice  will  not  be 
found  difficult  for  the  curved  letters.  There  are,  how- 
ever, letters  which  require  attention  in  almost  every 

LAFAYETTE 

Fig.   17 

arrangement  in  which  they  occur.  In  Fig.  17  is  shown 
a  word  involving  A,  F,  L,  T,  and  Y,  all  of  which, 
together  with  J,  P,  and  V,  are  difficult  to  combine  with 
other  letters  and  maintain  good  spacing  because  they 
differ  so  greatly  in  width  at  the  top  and  bottom.  When 
L  comes  before  A  it  is  wise  to  decrease  its  width  one-quar- 
ter unit.  So,  also,  when  T  follows  F,  P,  T,  V,  W,  or  Y,  its 
width  should  be  reduced  one-quarter  unit.  A  after  F  and 
before  or  after  T,  V,  W,  or  Y,  should  be  set  much  closer 
than  when  used  with  other  letters,  in  some  cases  the 
spacing  being  even  negative,  i.  e.,  the  F  overlapping  the 
A,  Fig.  17.  Other  changes  will  suggest  themselves. 

Crowding  Letters.  One  of  the  common  errors  made 
by  beginners  is  that  of  crowding  the  straight  stroke 

MINING  MINI  NO 

Approved          Spacing 
Incorrect    Spacing 

Fig.    18 

letters  too  close  together  and  separating  the  oval  letters 
too  far;  this  always  results  in  making  the  inking  look 
heavier  in  some  places  than  in  others,  Fig.  18. 


22  MECHANICAL  DRAFTING. 

Spacing  of  Compressed  and  Extended  Letters.  In  the 
latter  part  of  Art.  3  it  was  shown  that  wide  variation  in 
the  resulting  appearance  of  an  alphabet  may  be  secured 
by  modifying  the  proportions  of  the  oval  element.  It 
should  be  kept  in  mind,  when  performing  an  exercise  in 
any  altered  style,  that  good  appearance,  i.  e.,  uniformity 
of  shapes,  equality  of  spacing,  smoothness  of  effect,  can 
be  produced  in  only  one  way:  All  letters  and  spaces 
must  be  reduced  or  enlarged  in  the  same  proportion. 
That  is,  if  the  letters  are  decreased  one-third  their  normal 
widths  then  the  values  given  in  Fig.  16  must  be  decreased 
one-third  also,  in  order  to  give  the  proper  spacing  to  be 
used.  Thus,  suppose  the  word  shown  in  Fig.  19  (a) ,  if  con- 
structed of  normal  letters,  is  found  to  be  either  too  long 
or  too  short  for  the  space  available  for  it.  In  (b)  and 
(c)  of  this  figure  are  shown  the  same  word  constructed 

TERMINAL    STATION     TERMINAL  STATION 
TEIRK/IIMAL.      STVVTIOM 

(e) 

Fig.   19 

in  compressed  and  extended  styles  respectively.  In  each 
form,  however,  it  will  be  seen  that  the  distance  between 
straight  stroke  letters,  as  that  between  M  and  I,  conforms 
to  that  prescribed  in  Art.  8;  that  is,  it  is  one-third  the 
width  of  the  letter  M.  The  values  given  in  the  table, 
Fig.  16,  may  be  used  directly  by  simply  taking  as  the  unit 
for  spacing  one-sixth  the  width  of  the  M  in  the  particular 
style  used.  The  stems  of  compressed  and  extended  let- 
ters have  the  same  width  as  the  stems  of  normal  letters, 
i.  e.,  one- sixth  of  the  height.  The  method  here  outlined 
is  applicable  to  both  vertical  and  slant  styles. 


LETTERING. 

Mechanical  Spacing.  In  the  table,  Fig.  16,  is  given  in 
terms  of  a  sub-division  of  the  standard  unit  space,  the 
spacing  that  is  approximately  correct,  according  to  good 
design,  for  any  combination  of  letters.  If  this  table  be 
given  some  careful  study  in  connection  with  the  principle 
explained  in  the  paragraph,  " Method  of  Areas,"  it  will 
be  possible  after  some  little  practice  to  design  rapidly 
without  constant  reference  to  the  table  for  the  correct 
spacing. 

NAME   PLATES 

(9)  Definition,     A  name  plate  is  a  small  metal  plate 
fastened  to       machine  or   structure  and   should  contain 
the  following  information :  Name  of  the  machine  (unless 
it  is  so  common  as  to  be  perfectly  familiar  to  everyone), 
name  of  the  manufacturing  company,  and  address  or 
location  of  the  company's  works  or  factories. 

DRAWING  TITLES 

(10)  Definition.     A  working  drawing  title  is  a  con- 
densed statement  of  the  following  information:    Name 
of  the  piece  of  machinery  drawn,  name  and  address  of 
the  manufacturing  company,  initials  of  the  draftsman, 
checker,  and  tracer,  scale,  drawing  number,  and  other 
necessary  filing  data. 

GENERAL  ORDER  OF  WORK  IN  CONSTRUCTION  OF 
WORKING  DRAWING  TITLE 

(11)  Given  data.     In  making  up  a  working  drawing 
title  the  draftsman  ordinarily  has  given  him  a  certain 
amount  of  data  as  follows:    "Details  of  Horizontal  Mill- 
ing Machine,  manufactured  by  the  Landis  Tool  Company, 
Waynesboro,  Penna. ;  drawn  by  (B.  C.  S.),  checked  by 
( )f  traced  by  ( ),  scale  V2"=l",  draw- 


24  MECHANICAL  DRAFTING. 

ing  finished  April  2nd,  1915."  The  above  material,  con- 
densed, must  be  placed  within  a  given  title  space,  per- 
haps 3"x5". 

Elimination  of  unnecessary  material  and  arrange- 
ment into  groups.  In  order  that  the  given  material  may 
be  placed  within  the  given  title  space,  every  unnecessary 
word  must  be  eliminated.  Eunning  thru  the  given  data 
it  is  seen  that  the  words  italicized  can  be  omitted 
without  the  least  danger  of  misunderstanding  the 
remainder.  With  these  words  omitted  the  remaining 
data  seems  to  group  itself  naturally  as  follows: 

(1st  prom.)    Horizontal  Milling  Machine. 

Details 

(2nd  prom.)  Landis  Tool  Co. 

(3rd  prom.)  Waynesboro,  Pa. 

Drawn  by  ( ),  Checked  by  ( ),  Traced  by  ( ), 

(4th  prom.)      Date  ( ),  Scale  ( ). 

Order  of  prominence.  In  a  drawing  title  as  well  as 
in  a  name  plate,  certain  groups  of  words  are  more  impor- 
tant than  others.  In  the  drawing  title  the  name  of  the 
piece  of  machinery  is,  of  course,  given  most  prominence ; 
while,  in  the  case  of  the  name  plate  the  name  of  the  manu- 
facturing company  should  be  given  first  prominence.  In 
the  drawing  title  the  name  of  the  manufacturing  com- 
pany will  be  given  second  prominence,  address  of  the 
company  third,  and  the  remaining  information,  being 
about  equally  important,  should  be  given  least  prom- 
inence and  arranged  as  desired.  The  word  "Detail"  or 
"Assembly",  which  may  be  either  included  or  omitted 
as  desired,  will  not  figure  in  the  order  of  prominence. 


LETTERING.  25 

Methods  of  securing  prominence.  In  both  advertis- 
ing and  drafting  there  are  in  nse  two  methods  for  secur- 
ing prominence  of  any  one  group  of  words  over  another. 
The  one  most  generally  used  is  variation  in  height  of 
the  letters  of  the  various  groups,  to  correspond  in  general 
to  the  order  of  prominence  established;  if  this  is  not 
possible  thru  lack  of  space,  a  distorted  letter,  either  of 
odd  construction  or  of  the  compressed  or  expanded  style, 
may  be  used.  One  may  then  depend  on  the  odd  appear- 
ance of  the  letters  to  give  to  that  group  of  words  the 
desired  prominence.  In  the  case  of  drawing  titles  and 
name  plates  the  first  method,  i.e.,  variation  in  height  of 
letters  is  preferable. 

Margins  and  margin  lines.  Before  sketching  in  the 
guide  lines  for  the  various  groups  of  words,  margin 
spaces  should  be  determined  and  light  margin  lines  ruled 
in  Fig.  20.  In  doing  this  certain  rules  of  design  must  be 
adhered  to ;  the  upper  and  lower  margins  may  be  of  any 
desired  width;  however,  for  best  appearance  they  must 
be  equal.  The  right  and  left  margins,  tho  not  necessarily 
equal  to  the  upper  and  lower,  must  be  equal  to  each  other. 
In  a  rectangular  space  whose  width  is  greater  than  the 
height,  better  effect  is  obtained  if  the  right  and  left  mar- 
gins are  made  slightly  greater  than  the  upper  and  lower; 
if  the  reverse  is  true  of  the  rectangle  then  the  right  and 
left  margins  should  be  less  than  the  upper  and  lower. 

Guide  lines.  To  obtain  the  guide  lines  for  the  various 
groups  of  words,  produce  the  lower  margin  line  to  the 
left  until  it  intersects  the  border  of  the  title  space  at  A, 
Fig.  20,  and  from  this  point  draw  up  and  toward  the 
right  a  line  at  an  angle  of  about  60  degrees  with  the 
horizontal.  Selecting  any  desired  distance  as  the  rela- 


MECHANICAL  DRAFTING. 


! 

h 

1 

1 

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-iJ 

zj 

id 

o 

a 

p 

1 
1 

^ 

Zi 
Z 

N 

; 

i 

u 

[ 
i 

§ 

s 

ni 

1 

1 

1 
1 

1 

p 

R 

1 

O 

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1 
1 

d 

Zj 

U' 

J 

1 
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V.WAYMEBBDHO: 

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QJ 

13 
O 

LETTERING.  27 

tive  height  of  the  letters  of  the  lower  group,  lay  off  this 
distance  from  A  along  the  60  degree  line;  then  a  relative 
distance  for  the  space  between  this  line  and  the  line  next 
above;  next  a  relative  space  for  the  letters  of  the  next 
group  and  so  on  until  all  of  the  groups  have  been 
accounted  for  along  the  60  degree  line.  From  the  last 
point,  B,  draw  a  line,  B  C,  as  shown  in  figure  and  from 
the  various  points  along  the  line  A  B  draw  lines  parallel 
to  B  C  until  they  intersect  the  border  line,  A  C;  the  re- 
quired guide  lines  will  then  be  found  the  same  relative 
distances  apart  as  the  points  plotted  on  the  line  A  B. 


W        '    A 

y        N 

"    f    '  ' 

s   '  '   a   ' 
Scratch 

1     0      '  '   R 

Paper 

1  '  o    ' 

1  P  "  » 

Guide    Lines 


e        s          B        o 
Scratch    Paper 


Fig.  21 

Spacing  of  letters.  Before  attempting  to  place  in  any 
of  the  letters  the  value  of  the  unit  spaces  of  the  various 
groups  of  letters  must  be  determined.  Tho  the  various 
lines  of  letters  may  not  require  all  of  the  horizontal  space 
allotted  to  them,  for  best  appearance  they  must  be  placed 
centrally ;  i.e.,  with  equal  margins  at  their  right  and  left. 
To  accomplish  this,  rule  in  a  vertical  center  line  of  the 
title  space  and  use  the  following  method : 

Scratch  paper  method.  Select  any  point  close  to  the 
left  end  of  the  straight  edge  of  a  sheet  of  scratch  paper, 


28  MECHANICAL  DRAFTING. 

Fig.  21,  and  from  this  point  step  off  with  the  large  and 
small  dividers  the  proper  number  of  unit  spaces  in  suc- 
cession, for  the  various  letters  and  spaces  between  letters, 
marking  with  the  divider  points  the  location  of  the 
beginning  and  end  of  each  letter.  Placing  the  scratch 
paper  centrally  along  the  lower  guide  line  of  the  space 
into  which  this  group  of  letters  is  to  go,  mark  with  the 
needle  point  the  position  of  the  beginning  and  end  of 
each  of  the  letters.  This  method  has  the  advantage  of 
centrally  placing  the  entire  group  and  of  locating  the 
various  letters  at  the  same  time. 

If  the  letters  are  to  be  free  hand  the  above  method 
will  be  found  equally  useful.  Instead  of  laying  off  the 
spaces  in  units,  the  letters  themselves  should  be  sketched 
on  the  scratch  paper  and  the  group  placed  centrally  as 
before.  The  style  of  letters  to  be  used,  i.e.,  normal,  com- 
pressed or  extended,  will  be  readily  suggested  by  this 
procedure. 

Bill  of  material.  On  detail  drawings  where  numerous 
pieces  are  shown,  a  bill  of  material  should  be  placed 
above,  and  usually  joined  to  the  title.  In  general  it 
should  contain  in  tabular  form  such  information  as — 
the  number  of  pieces  required,  material  made  of,  pat- 
tern numbers,  part  numbers,  name  of  pieces,  and  other 
information.  Examples  of  typical  bill  of  material  will 
be  found  in  the  Appendix. 

GUMMED  LETTERS 

(12)  For  those  who  have  an  appreciable  amount 
of  work  on  titles,  signs,  etc.,  the  gummed  letters  sold  by 
the  Ticket  and  Tablet  Company,  of  Chicago,  and  which 
are  shown  in  their  exact  sizes  and  styles  in  the  appendix, 
will  be  found  a  great  convenience.  The  many  uses  which 
such  letters  serve  need  not  be  enumerated.  They  are 
made  in  red,  white,  and  black. 


USE  OF  INSTRUMENTS. 


29 


CHAPTER  2 

USE  OF  INSTRUMENTS 
DRAWING-BOARD 

(13)  Construction.  Drawing-boards  are  made  of 
either  poplar  or  white  pine,  the  right  and  left  edges,  Fig. 
1,  being  reinforced  by  cleats  of  some  harder  wood.  These 


hard  wood  cleat 


DRAFTING  ONLY 


Fig.   1 


cleats  serve  both  as  stiffeners  and  as  runners  for  the  easy 
sliding  of  the  T-square.     The  better  grades  of  small 


Maple  or  celluloid  strip 


Fig.   2 


boards  are  reinforced  on  the  back  by  two  battens,  Fig.  2, 
and  ordinarily,  have  inserted  in  their  right  and  left  edges 
a  wearing  strip  of  either  hard  maple  or  celluloid,  instead 
of  the  cleats  of  Fig.  1.  It  will  be  noticed  in  Fig.  2  that 


30 


MECHANICAL  DRAFTING. 


the  right  and  left  edges  of  the  second  class  of  board 
are  broken  at  intervals  by  saw  cuts  which  prevent  the 
inserted  strip  of  hard  wood  from  expanding  and  split- 
ting the  wood. 

Use.  The  two  sides  of  the  type  of  board  shown  in 
Fig.  1  have  very  definite  uses  if  the  board  is  to  be  kept 
in  shape  for  good  drafting.  The  one  side  for  drafting 


1°                             ° 

Head  of  T-square  ALWA\ 

S  to  LEFT              0  | 

Paper 
o                                             0 

Tacks  about  %"  from 
edges  of  sheet 

Position  when  not  in  use 

I 

Fig.  3 

only,  the  other  for  any  necessary  rough  work,-  trimming 
paper,  etc.    Never  trim  paper  on  the  drafting  side. 

PAPER 

(14)  Quality.  A  novice  cannot  obtain  good  work 
from  poor  material,  hence  it  is  imperative  that  the  begin- 
ner in  drawing  use  the  best  quality  of  paper  obtainable. 
A  heavy,  hard  surface  paper  of  the  quality  of  Keuffel  & 
Esser's  Normal,  or  E.  Dietzgen's  Napoleon  is  recom- 
mended. 

Position  of  paper  on  board.  In  tacking  the  paper  to 
the  board,  Fig.  3,  keep  the  sheet  well  toward  the  top  and 


USE  OF  INSTRUMENTS. 


31 


to  the  left;  about  two  and  one-half  inches  from  the  upper 
and  left  edges.  This  should  be  done  in  order  that  the 
draftsman  may  work  to  advantage  on  the  bottom  of  the 
sheet,  and  that  it  may  not  be  necessary  to  work  to  any 
great  extent  on  the  end  of  the  T-square  blade,  which 
cannot  be  prevented  from  springing  slightly. 

Tacking  sheet.  Place  upper  left  corner  of  sheet  in 
approximately  correct  position  and  tack  to  the  board, 
Fig.  3,  placing  tacks  close  to  the  corners  of  the  paper. 
Then  after  lining  up  the  upper  edge  with  the  upper  edge 
of  the  T-square  blade,  stretch  sheet  and  tack  upper  right 
corner.  The  lower  edges  may  be  tacked  down  in  any 
order;  or,  after  some  experience,  may  be  left  untacked, 
as  these  tacks  have  a  tendency  to  interfere  with  the 
T-square  and  triangles. 


BORDER  LINES 

(15)  The  border  lines  as  well  as  all  other  construc- 
tion work  done  by  the  draftsman  should  be  placed  in  by 
measurements  from  center 

lines  and  not  from  the 
edges  of  the  sheet.  In  the 
case  of  the  border  lines, 
the  measurements  are 
made  from  the  horizontal 
and  vertical  center  lines  of 
the  sheet,  Fig.  4.  Fig  4 

T-SQUARE 

(16)  Construction.    Both  the  blade  and  the  head  of 
the  T-square,  Fig.  5,  are  of  hard  wood,  hence  the  glue 


1-4 

-e(— 

\ 
\ 

\ 

f 

'* 

\ 
\ 

L 

32 


MECHANICAL  DRAFTING. 


Walnut  or  Ebony  Head 


joint 


Fig.  5 


cannot  cement  them  very  tightly  together ;  neither  do  the 
short  screws  hold  very  firmly;  a  fall,  even  to  the  floor, 
may  break  the  joint  and  damage  the  T-square.  Keep  the 
T-square  out  of  danger  of  any  such  fall. 

In  case  the  joint 
breaks,  take  out 
screws,  rough  both 
head  and  blade  with 
coarse  sandpaper, 
coat  well  with  Denni- 
son's  glue,  place 
blade  at  90°  with  head 
with  triangle,  tighten 
screws  and  let  stand 
a  day.  Then  take  out  screws  and  put  in  round-headed 
wood  screws  long  enough  to  run  through  and  project  an 
eighth  of  an  inch  or  more.  File  off  screws  carefully.  Be 
sure  screws  are  tight.  It  may  be  advisable  to  bore  small 
holes  entirely  through  head  and  blade  for  these  large 
screws,  to  prevent  splitting  of  the  wood. 

Position  on  board.  In  drafting,  a  right-handed  man 
should  keep  the  head  of  the  T-square  to  the  left,  Fig.  6, 
in  order  that  he  may  handle  it  with  his  left  hand,  leaving 
the  right  free  for  drafting.  Never  place  the  T-square  in 
any  other  position  on  the  board,  as  the  edges  of  the  board 
seldom  form  a  rectangle  nor  is  the  head  of  the  T-square 
likely  to  make  exactly  90  degrees  with  the  blade. 

Use  of  blade.  The  upper  edge  of  the  blade  should  be 
used  for  drafting  only;  and  the  draftsman  will  do  well 
to  take  excellent  care  of  this  edge,  for  once  nicked  or 


USE  OF  INSTRUMENTS. 


33 


dented  the  instrument  is  practically  ruined  for  good  work. 
The  lower  edge  may  be  used  as  a  cutting  ruler  but  never 
for  drafting. 


ALWAYS  to  LEFT 


o! 


Fig.   6 


Position  when  not  in  use.  Any  draftsman  profits  by 
keeping  his  drawing  instruments  in  certain  definite 
places,  so  that  as  far  as  possible  he  may  keep  his  atten- 
tion entirely  on  his  work,  handling  his  instruments  sub- 
consciously. It  is  found  most  convenient  to  slip  the 
T-square  to  the  bottom  of  the  board,  when  not  in  use ;  it 
is  here  out  of  danger,  out  of  the  way,  yet  easily  accessible. 

To  keep  clean.  A  drawing  may  easily  be  smudged  by 
a  dirty  T-square,  so  it  will  be  well  to  give  the  blade  a 
thoro  cleaning  with  a  damp  cloth  or  piece  of  art  gum  at 
frequent  intervals. 


84  MECHANICAL  DRAFTING. 

SCALE 

(17)  Care.  The  scale  should  never  be  used  as  a 
ruler  because,  as  a  drafting  instrument  its  efficiency 
depends  upon  the  condition  of  its  edges,  and  these  edges 
can  easily  be  defaced  by  misuse  and  the  instrument  badly 
damaged.  Furthermore,  the  boxwood  of  which  the  scale 
is  made  warps  quite  easily;  hence,  the  edges  of  a  tri- 
angular scale  will  seldom  be  found  perfectly  straight. 


Fig-   7 

Use.  On  inspection,  Fig.  7,  it  is  seen  that  the  numer- 
als are  all  placed  on  the  scale  so  as  to  appear  upright 
only  when  one  works  over  the  top  of  the  scale  or  on  the 
edge  away  from  the  draftsman  and  not  toward  him.  All 
dimensions  should  be  taken  directly  from  the  scale  as  it 
lies  on  the  drawing  and  not  by  means  of  the  dividers. 
The  needle  point  is  the  best  aid  in  obtaining  dimensions 
with  perfect  accuracy.  The  pencil  point  is  a  poor  sub- 
stitute for  the  needle  point. 

NEEDLE  POINT 

(18)  From  Richter  type  of  instruments.  An  excel- 
lent needle  point  for  obtaining  dimensions  may  be  made 


USE  OF  INSTRUMENTS. 


35 


up  by  inserting  into  the  long  knurled  barrel  furnished 
with  every  set  of  Bichter  type  of  instruments,  the  small 
point  which  is  provided  for  converting  the  large  compass 
into  a  set  of  dividers,  Fig.  8. 


To  make  in  shop.  A  needle  point  may  be  easily  made 
from  a  strip  of  white  pine  i4//x1/4'/x2//  and  a  medium  size 
sewing  needle. 


Fig.  9 


Construction:    Fig.  9.    Insert  the  needle  in  a  vise, 
point  down,  with  about  %"  of  the  point  in  the  vise,  and 


36 


MECHANICAL  DRAFTING. 


carefully  drive  the  strip  of  pine  over  the  exposed  part 
of  the  needle;  the  wood  may  then  be  shaved  round  and 
pointed  slightly  at  the  needle  end. 

TRIANGLES 

(19)  In  drawing  vertical  lines  with  triangles  the  ver- 
tical edge  should  always  be  to  the  left  or  toward  the 
head  of  the  T-square,  Fig.  10. 

To  clean.    The  surface  of  the  celluloid  tri- 
angles quickly  becomes  smudged  from  era- 
sings  and  pencil  dirt  that  may  be  on  the 
drawing;  hence,  they  must  be  cleaned 


A 


Fig.   10 


Fig.   11 


frequently  with  soap  if  the  drawings  are  to  be  kept  in 
good  shape. 

Letter  guide  lines.  For  the  easy  ruling  of  letter  guide 
lines  without  the  use  of  the  scale  and  needle  point,  it  is 
suggested  that  along  the  edges  of  the  30x60  triangle 
light  lines  be  scratched  with  the  needle  point  as  follows : 
Along  the  hypothenuse  and  1/8"  from  the  edge  scratch 
carefully  a  fine  line;  also  a  second  line  3/16"  from  the 


38 


MECHANICAL  DRAFTING. 


about  one  inch  from  the  ends,  leaving  about  1,4"  of  the 
lead  exposed,  Fig.  15.  One  end  is  to  be  sharpened  to  a 
round  point,  the  other  to  a  wedge.  In  shaping  up  both 
of  these  points,  use  the  pencil  point  file  provided  in 
the  kit. 


Fig.    13 


Fig.   14 


Round  point.  In  shaping  up  the  round  point,  hold 
the  pencil  at  an  angle  of  about  45  degrees  with  the  axis 
of  the  file.  As  the  lead  travels  over  the  file,  Fig.  16, 
revolve  the  pencil  slowly  between  the  thumb  and  fingers, 


USE  OF  INSTRUMENTS. 


39 


attempting  to  give  it  a  complete  revolution  with  each 
stroke.  The  lead  may  thus  be  easily  sharpened  to  a  per- 
fect .cone.  In  this  sharpening  be  careful  that  the  point 
extends  the  full  length  of  the  lead  exposed. 


Fig.  15 


Fig.  16 


Wedge  point.     In  sharpening  the  wedge  point  hold 
the  pencil  perpendicular  to  the  axis  of  the  file,  Fig.  17, 


Bound  point 


Fig.   17 


and  so  inclined  to  the  plane  of  the  file  that  the  lead  may 
be  sharpened  the  full  quarter  inch  exposed. 


40 


MECHANICAL  DRAFTING. 


Use  of  points.  The  round  point  should  be  used  for 
drawing  short  lines  and  lettering,  the  wedge  point  for 
long  lines;  the  round  point  dulls  rapidly  in  drawing  a 
long  line  and  will  make  a  line  of  varying  weight. 

ERASERS 

(21)  If  an  eraser  becomes  apparently  greasy  and 
smudges  instead  of  cleans  a  drawing,  it  may  easily  be 
cleaned  by  rubbing  it  with  another  eraser  or  by  rubbing 
it  on  the  rough  surface  of  the  drawing-board  itself. 


Fig.  18 

CLEANING  PADS  AND  BLOTTERS 

(22)  Chamois  roll  or  block.  Inasmuch  as  water 
proof  drawing  ink  dries  so  rapidly  the  pen  should  be 
cleaned  thoroly  with  cloth  or  chamois  before  each  refill- 
ing. In  addition  to  this  cleaning  it  will  be  found  possi- 
ble to  obtain  more  clear  cut  work  if  after  each  three  or 
four  lines  the  point  of  the  pen  is  scraped  over  a  piece 
of  chamois.  A  convenient  cleaner  may  be  made  by  roll- 


USE  OF  INSTRUMENTS.  41 

ing  up  a  2"x4"  piece  of  chamois  and  binding  it  with  a 
rubber  band,  Fig.  18,  or  by  pasting  a  2"x  2"  piece  on  a 
small  block  of  wood. 

Blotters.,  Never  attempt  to  blot  drawing  ink.  The 
ink  is  too  heavy  to  be  absorbed  by  blotting  paper. 
Always  permit  the  ink  to  dry.  A  puddle  of  ink  may, 
however,  be  removed  by  the  careful  use  of  the  corner  of  a 
blotter. 

LARGE  DIVIDERS 

(23)  Adjustment  of  the  points.  With  the  Richter 
type  of  instrument,  it  will  always  be  found  possible  to  ad- 
just the  points  of  the  various  tools  to  any  desired  length; 
so,  before  attempting  to  use  the  large  dividers  be  sure  that 
the  points  are  adjusted  to  exactly  the  same  length  and 
that  they  are  in  perfect  shape.  In  case  the  points  of  the 
Gem  Union  instruments  are  not  of  the  same  length,  it 
will  be  necessary  to  grind  the  long  point  down  on  a  small 
carborundum  stone.  Keep  points  always  in  perfect  shape 
for  good  work. 

Opening  and  setting.  It  is  desirable  always  to  handle 
each  instrument  with  the  right  hand  unaided  by  the  left; 
this  permits  of  much  more  rapid  work  and  the  habit  is 
not  difficult  to  acquire.  To  open  the  divider,  insert  the 
thumb  between  the  legs,  prying  them  apart  a  short  dis- 
tance until  the  fingers  may  be  inserted  and  the  one  leg 
grasped  between  the  first  and  second  fingers,  the  other 
between  the  third  finger  and  the  thumb;  the  head  of  the 
instrument  should  rest  against  the  knuckle  of  the  first 
finger.  Holding  the  instrument  in  this  position  it  is 
found  easily  possible  to  adjust  the  points  to  any  desired 
distance. 


42 


MECHANICAL  DRAFTING. 


To  place  point.  To  place  the  one  point  of  the  divider 
at  any  point  on  the  sheet,  rest  the  wrist  at  a  convenient 
distance  from  the  point ;  it  will  then  be  found  easily  pos- 
sible to  place  the  point  of  the  leg  between  the  third  finger 
and  the  thumb  in  any  desired  position.  Raising  the 
wrist  and  keeping  the  little  finger  on  the  paper,  the  other 
leg  can  now  be  adjusted  for  any  desired  distance.  It  is 
perhaps  as  good  practice  and  may  be  found  easier  for 
some  to  steady  the  hand  thruout  the  operation  by  merely 
resting  the  little  finger  on  the  paper,  instead  of  the  wrist. 

Stepping  off  distances.  After  the  points  have  been 
placed  as  desired,  to  step  off  a  certain  distance  a  num- 
ber of  times,  raise  the  first  finger  to  the  top  of  the  head, 
then,  releasing  the  other  leg,  grasp  the  head  between  the 
first  finger  and  the  thumb  and  step  off  the  distance  by 
swinging  the  dividers  alternately  over  and  under.  Hand- 
ling the  instrument  in  this  way  it  will  not  be  necessary 
to  take  a  new  grip  on  the  head  thruout  the  operation. 

LARGE  COMPASS 

(24)  Adjustment.  To 
adjust  the  needle  point  of 
a  compass  to  both  the  pen- 
cil and  pen,  remove  the 
pencil  point  and  insert 
pen;  after  adjusting  the 
needle  point  so  that  its 
shoulder,  not  the  point,  is 
flush  with  the  end  of  the 
pen,  remove  pen  and  in- 
serting pencil,  adjust  lead 
until  it  is  even  with  the  shoulder  of  the  needle  point. 


Wedge  point 


Fig.    19 


USE  OF  INSTRUMENTS.  43 

Use.  For  adjustment  of  leads  to  any  desired  radius, 
and  placing  needle  point  at  any  desired  center,  see  Large 
Dividers,  Art.  23.  For  describing  arcs  with  the  large 
compass  the  legs  should  be  adjusted  as  shown  in  Fig.  19. 

IRREGULAR  CURVE 

(25)  The  irregular  curves  are  those  which  cannot  be 
drawn  readily  and  accurately  with  the  compass.  The  gen- 
eral directions  of  the  different  portions  of  such  curves  are 
first  determined  roughly  by  a  number  of  plotted  points 
at  as  small  intervals  as  possible  (the  positions  of  these 
points  are  obtained  either  by  mathematical  coordinates 
or  mechanically  from  other  projections  or  views  of  the 
same  curve).  Before  drawing  the  curve  mechanically  it 
is  best  to  draw  lightly  a  freehand  curve  thru  the  plotted 
points,  then  carefully  piece  by  piece  the  mechanical 
curve  may  be  drawn.  In  drawing  the  mechanical  curve 
two  things  must  be  kept  in  mind;  first,  that  the  final 
curve  must  coincide  as  absolutely  as  possible  with 
the  freehand  curve;  second,  that  the  curve  must  be 
"smooth,"  i.  e.,  it  must  have  no  sudden  glaring  changes 
of  curvature  or  "humps."  The  failure  of  a  novice  to 
obtain  a  good  irregular  curve  is  due  to  perhaps  two 
causes:  first,  that  he  starts  with  the  assumption  that  it 
is  too  easy  to  require  any  attention,  and  second,  that  he 
is  too  easily  satisfied  with  a  very  indifferent  job.  Curves 
having  curious  "humps"  may  be  termed  freaks  and  are 
seldom,  if  ever,  encountered  in  Mechanics. 

It  is  difficult  to  recommend  any  curve  or  even  several 
curves  as  being  even  approximately  universal,  so  no  such 
advice  will  be  attempted.  A  great  number  of  such  curves 
are  listed  in  all  instrument  catalogs  and  special  require- 
ments will  have  to  be  depended  upon  in  any  selection. 


MECHANICAL  DRAFTING. 


However,  two  curves  have  found  much  favor  among  stu- 
dents and  are  recommended  for  general  use.  One  of 
these  has  obtained  the  name  of  "Banana"  curve,  Fig.  20, 
and  the  other  is  the  Gr.  E.  D.  Special,  Fig.  21. 


Fig.  20 


Fig.  21 


BOW  DIVIDERS 

(26)     Adjustment.     (See     Adjustment    for     Large 
Dividers.) 

Placing  at  center.     (See  same  for  Large  Dividers.) 

Opening  and  closing  points.    With  the  center  adjust- 
ment instrument,  which  is  always  preferable  to  the  side 


USE  OF  INSTRUMENTS.  45 

adjustment,  after  placing  the  one  point  at  a  given  point 
on  the  sheet,  raise  the  first  finger  to  the  head  and  turn 
the  adjustment  screw  between  the  second  finger  and 
thumb  until  the  points  are  apart  as  desired. 

Stepping  off  distances.  (See  same  for  Large 
Dividers.) 

BOW  PENCIL 

(27)  Hard  lead.  To  obtain  satisfactory  work  from 
the  bow  pencil  the  lead  should  be  extremely  hard,  at  least 
6H.  Ordinarily,  the  lead  supplied  with  instruments  is 
not  more  than  2H  or  3H,  and  wears  down  too  rapidly. 
Try  the  lead  before  using  it  on  a  drawing,  and  if  found 
soft,  substitute  for  it  a  piece  of  lead  from  a  6H  pencil. 

Sharpening  lead.  Since  the  bow  pencil  is,  like  the 
bow  dividers,  an  instrument  of  precision,  for  small  arcs 
the  round  point  will  be  found  more 
convenient  than  the  wedge.  Inas- 
much as  the  total  amount  of  use  is 
small  compared  with  that  of  the 
large  compasses,  the  need  of  a 
wedge  point  to  diminish  the  number 
of  times  required  to  shape  it  up,  is 
not  great  enough  to  overbalance  the 
inaccuracy  and  awkwardness  of  the 
latter  in  drafting.  It  is  well  to  Fig.  22 

shape  the  point  as  long  as  the  con- 
struction of  the  instrument  and  the  strength  of  the  lead 
will  permit.    Fig.  22. 

Adjustment  to  any  radius.   In  adjusting  thepowte  to  any 
desired  radius, instead  of  obtaining  the  dimension  directly 


46 


MECHANICAL  DRAFTING. 


from    the    scale,    it    will    be    better    to    transfer    this 
radius  to  the  paper  by  means  of  the  scale  and  needle 
point,  and  set  the  bow  pencil  from 
this  as  explained  under  Large  Di- 
viders. 


Describing  arcs.  In  describing 
an  arc  with  either  the  compass,  bow 
pencil  or  pen,  the  direction  of  mo- 
tion of  the  lead  should  be  clockwise 
and  thru  the  total  length  of  the  de- 
sired arc  before  taking  the  point 
from  the  paper,  Fig.  23. 

RULING  PEN 

(28)  Manner  of  holding.  The 
ruling  pen  should  be  held  between 
the  first  and  second  fingers  and 
thumb  as  shown  in  Fig.  24.  In 
ruling  lines,  the  adjusting  screw 
should  be  turned  from  the  user. 


Fig.   23 


Position  of  pen.    Unless  care  is 
taken  to  keep  the  pen  in  a  vertical 
plane  thru  the  edge  of  the  T-square 
blade  or  edge  of  the  triangle,  Fig.  25,  trouble  may  be  ex- 
perienced in  the  ink  running  under  the  T-square  blade, 
Fig.  26,  or  in  a  badly  broken  line,  Fig.  27. 

Tilted  in  the  direction  of  motion.  For  best  results 
the  pen  should  be  tilted  slightly  in  the  direction  of  the 
motion,  Fig.  24;  this  permits  one  to  inspect  the  work  of 


USE  OF  INSTRUMENTS. 


47 


the  pen  as  it  travels.  A  greater  angle  than  10  or  15 
degrees  may  however  permit  the  ink  to  run  down  and 
cause  a  blot. 


\ 

7 

*\ 

I3I 

\\    1 
\\   «§ 
VA 

vx\ 

c/    / 

£// 

?'/ 

VA 

// 

T\i 

yf 

'fVf 

ty 

1 

// 

*1W////////1£     \ 

Fig.  24 


Fig.  25 


Effect  of  Position  2 


Effect  of  Position  3 


Ink  ran  under  T  squar 

Fig.   26 


Pen  riding  on  one  nib 
Fig.   27 


To  fill  pen.  To  fill  the  pen,  always  use  the  quill  sup- 
plied on  the  stopper  of  the  ink  bottle.  Never  dip  the  pen 
into  the  ink.  If  by  chance  any  ink  has  gotten  on  the  out- 
side of  the  pen,  wipe  it  off  carefully  before  using;  it  may 
save  a  serious  blot. 


MECHANICAL  DRAFTING. 


Direction  of  motion  in  ruling  lines.  In  ruling  lines, 
either  with  the  pen  or  pen- 
cil, the  direction  of  motion 
should  be  from  left  to  right 
or  from  bottom  to  top  of  the 
sheet,  Fig.  28.  Ruling  lines 
thus,  it  is  always  possible  to 
see  what  the  pen  or  pencil 
is  doing.  Never  rule  lines 
down  the  sheet  unless  they 
are  oblique  and  are  being  put  in  with  the  triangle. 


Fig.   29 


INK  BOTTLES 

(29)  Holder.  A  convenient  holder  for  the  ink  bot- 
tle may  be  made  from  two  sheets  of  blotting  paper  and 
a  rubber  band  as  shown  in  Fig.  29.  A  holder  of  some 


USE  OF  INSTRUMENTS. 


49 


50 


MECHANICAL  DRAFTING. 


Fig.   30 


kind  is  advisable  and  one  such  as  this  answers  a  double 
purpose.  A  holder  of  the  style  shown  in  Fig.  30  may  be 
purchased  from  any  of  the  instrument  companies. 

Closed  when  not  in 
use.  India  ink  is  very 
heavy  and  dries  quite 
rapidly;  hence,  if  the 
stopper  is  left  out  of  the 
bottle  even  for  several 
hours  the  ink  may  be- 
come so  heavy  as  to 
make  it  impossible  to 
obtain  good  work  from 
it.  Be  sure  to  close  the  bottle  carefully  after  each  refill- 
ing of  the  pen.  With  proper  treatment  the  ink  will 
remain  in  good  condition  for  several  years. 

To  open  bottle  and 
fill  pen.  To  open  the 
bottle  without  danger 
of  upsetting,  grasp 
the  neck  between  the 
third  and  little  fin- 
gers, Fig.  31,  and  the 
stopper  between  the 
first  finger  and  thumb 
of  the  same  hand;  af- 
ter removing  the 
stopper,  place  the 
quill  between  the  nibs 
of  the  pen,  and  fill  as  desired.  If  too  much  ink  is  placed 
in  -the  pen  ragged  lines  and  perhaps  serious  blots  will  be 
the  result. 


Fig.  31 


LIBRARY 

STATE  NORMAL  SCHOOL 


l< 


(30)     The  protractor  in  most  general  use  is  a  semi- 
of  celluloid,  horn  or  metal  whose  circumference  is 
^divided  into  degrees  and  perhaps  half  degrees.     On  the 


Fig.   32 

Line-0-Graph,  Fig.  32,  is  shown  a  90°  protractor  which 
j\  without  any  handicap  can  be  substituted  for  the  usual 
^180°  instrument.  To  measure  any  desired  angle,  the 
£j  center  of  the  circle  is  placed  at  the  vertex,  and  0°  on  one 
*""  side  of  the  given  angle.  The  value  of  the  angle  may 
^  then  be  read  directly  from  the  quadrant. 


52  MECHANICAL  DRAFTING. 

CHAPTER  3 

ORTHOGRAPHIC  PROJECTION 

(31)  Definition.     An  orthographic  projection  of  any 
object  is  such  a  representation  on  a  given  plane  (usually 
vertical  or  horizontal)  as  will  show  in  true  proportion 
the  contours  of  the  object  as  seen  in  a  direction  perpen- 
dicular to  the  plane;  i.  e.,  as  though  viewed  from  an  in- 
finite distance,  when  all  the  lines  of  sight  would  be  paral- 
lel to  each  other  and  perpendicular  to  the  plane  of  pro- 
jection. 

PRINCIPLES  OF  ORTHOGRAPHIC  PROJECTION 

(32)  It  is  seen  from  Fig.  1,  which  is  a  representation 
of  a  machine  part  that,  tho  the  object  is  represented  as 
we  are  accustomed  to  see  it,  the  picture  gives  us  abso- 
lutely no  conception  of  the  ratio 

of  the  several  parts  of  the  object 
to  each  other;  i.  e.,  tho  the  sides 
of  the  square  hole  in  the  top  may 
appear  to  be  equal  to  the  thick- 
ness of  the  object,  one  has  no 
means  of  knowing  exactly  what 

the  relation  is;  hence,  unless  actual  dimensions  were  given 
for  every  detail  of  such  a  drawing,  and  these  dimensions 
could  be  depended  upon  to  be  absolutely  accurate,  one 
would  have  no  means  of  making,  except  approximately, 
the  object  which  the  drawing  represents.  Hence,  it  will 
be  appreciated  that  in  making  drawings  for  the  use  of 


ORTHOGRAPHIC  PROJECTION 


workmen  in  shops,  such  an  application  of  Descriptive 
Geometry  should  be  employed  as  will  represent  each  line 
of  the  object  at  least  once,  in  its  true  mathematical  ratio 
to  other  lines;  i.e.,  such  a  representation,  that  if  no 
dimensions  were  given,  one  could  compare  lines  by  means 
of  a  scale  or  dividers  and  be  certain  of  their  exact  ratio 
to  each  other.  This  branch  of  Descriptive  Geometry  is 
known  as  Orthographic  or  Proportional  Measurement 
Projection. 

Orthographic  projection.  To  obtain  such  a  projec- 
tion of  the  machine  part  represented  in  Fig.  1,  let  us  im- 
agine that  we  have  suspended  it 
in  space  with  the  face  containing 
the  square  hole  horizontal;  then, 
see  Fig.  2,  let  us  imagine  that 
four  planes  be  drawn  about  this 
machine  part  in  the  positions 
shown,  one,  a  horizontal  plane,  a 
second  a  vertical  plane  parallel 
to  the  face  A,  and  two  other 
planes  perpendicular  to  both  the 
vertical  and  horizontal  planes 
just  drawn. 

Pig.   2 

Coordinate  planes  and  coordi- 
nate angles.  The  three  planes  just  constructed  about  the 
machine  part  in  Fig.  2  are  known  in  orthographic  pro- 
jection as  coordinate  planes  and  are  named  individually, 
the  Horizontal  or  H  plane,  Vertical  or  V  plane,  Profile  or 
End  plane;  see  Fig.  3.  The  four  dihedral  angles  formed 
by  the  H  and  V  planes  are  known  as  1st,  2nd,  3rd,  and  4th 
and  are  numbered  in  the  order  shown. 


54 


MECHANICAL  DRAFTING. 


Projections  or  orthographic  representations.  In  ex- 
plaining the  method  used  in  obtaining  the  orthographic 
representations  of  the  machine  part,  the  corner  A,  Fig. 
4,  will  be  taken  as  typical  of  all  significant  points  of 


First  Angle 
/' 
/       Ground 


Fourth  Angle 


Pig.  8 


the  object.  It  is  desired  to  represent  this  point  on  each 
of  the  three  coordinate  planes,  the  second  End  plane  be- 
ing for  the  time  eliminated.  From  point  A  are  dropped 
three  perpendiculars,  one  to  each  of  the  coordinate 
planes;  the  points  in  which  these  perpendiculars  pierce 


ORTHOGRAPHIC  PROJECTION 


55 


these  coordinate  planes  are  known  as  the  projections  of 
point  A,  and  are  called,  V  or  Vertical  projection  or 
Front  View  (always  lettered  a'  if  lettered  at  all),  H  or 
Horizontal  projection  or  Top  View  (always  lettered  a 
if  lettered  at  all),  and  Profile,  End  Projection,  End  or 
Side  View  (always  lettered  a"  if  lettered  at  all) ;  if  then 
from  all  of  the  points  of  the  object  perpendiculars  were 
dropped  to  the  Vertical  plane  and  lines  drawn  connecting 
the  piercing  points  of  these  perpendiculars  in  regular 


FIRST  ANGLE 
PROJECTION 


Fig.  4 

order,  Fig.  4,  we  would  have  on  the  Vertical  plane  a 
drawing  or  projection  representing  perfectly  the  appear- 
ance of  the  front  of  the  machine  part;  a  similar  process 
would  give  us  on  the  Horizontal  plane  a  correct  repre- 
sentation of  the  top  of  the  object  and  on  the  End  plane  a 
representation  of  the  side  of  the  object. 

1st  and  3rd  angle  projections.  If  the  object  be  placed 
in  the  1st  angle,  as  in  Fig.  4,  the  projections  referred  to 
above  are  known  as  first  angle  projections.  If  the  object 


56 


MECHANICAL  DRAFTING. 


is  placed  in  the  3rd  angle,  as  in  Fig.  6,  the  projections 
are  known  as  third  angle  projections;  i.  e.,  the  projections 
of  an  object  are  known  as  First  or  Third  Angle  projec- 
tions according  to  the  angle  in  which  the  object  is  placed. 
It  should  be  noted  that  Figs.  4  and  6  show  only  those 


£- 

\ 
\ 
\ 


V  Plan*                                        / 

a'        f 

a- 

I"]  1~| 

Elevation                 s 

\ 
1                         C" 

End  View 
P  Plane  Revolved 

i  7 

\    / 
i  / 

L                                                f 

/ 

s 

^' 

s*  ' 

^.-^ 

D\  ,.„ 

H  Phmc  Revolved                      x-^ 

Fig.  5 


parts  of  the  coordinate  planes  that  enclose  the  angle  of 
projection  under  consideration.  No  mention  is  made  of 
the  Second  or  Fourth  Angle  projections  because  it  would 
be  impracticable  to  use  either  as  working  drawings. 

Revolution  of  coordinate  planes.  Already  an  appar- 
ent difficulty  has  arisen  in  the  question  of  how  to  repre- 
sent all  of  these  projections,  e.g.,  of  point  A,  Fig.  4,  on  a 
single  sheet  of  paper  when  in  fact  the  three  projections, 
a,  a'  and  a" ,  are  found  on  three  planes  at  right  angles  to 


ORTHOGRAPHIC  PROJECTION  57 

each  other.  The  line  of  intersection  of  the  Horizontal 
and  Vertical  planes  is  known  as  the  Ground  Line  or  G  L; 
the  intersection  of  the  Vertical  and  End  planes  is  Crl  Llt 
This  difficulty  can  now  be  solved  as  follows :  Using  G  L 
as  an  axis,  Fig.  5,  let  us  imagine  that  the  portion  of  the 
H  plane  in  front  of  V  is  revolved  down  until  it  coincides 
with  the  V  plane.  It  should  be  remembered  that  the  por- 
tion of  the  H  plane  behind  (not  shown  in  the  Fig.)  re- 


THIRD  ANGLE 
PROJECTION 


Fig.  6 


volves  up  till  it  coincides  with  the  V  plane  above  G.  L.  In 
this  revolution,  a  revolves  into  the  new  position,  a,  on 
the  continuation  of  the  perpendicular  dropped,  from  a' 
to  G  L;  for,  if  thru  the  two  lines  Aa  and  Aa',  Fig,  4,  a 
plane  be  passed,  it  will  cut  from  the  V  plane  a  line 
thru  a'  perpendicular  to  G  L;  as  a  revolves  about  G  L 
down,  it  revolves  in  the  plane  of  Aa,  and  when  it  reaches 
the  V  plane,  must  lie  on  the  perpendicular  to  G  L  thru 
a',  the  line  cut  from  the  V  plane  by  the  plane  of  Aa.  Since 
a  is  before  G  L  the  distance  Aa',  a  will  be  found  below 
G  L  the  same  distance ;  a'  is  above  G  L  the  distance  A  a; 
hence,  the  distance  from  G  L  to  the  points  a  and  of  repre- 


58 


MECHANICAL  DRAFTING. 


sents  the  exact  distances  which  the  point,  of  which  these 
are  the  projections,  is  from  the  V  and  H  planes.  If  then, 
Gt  L,  be  used  as  an  axis  and  the  portion  of  the  Profile 
plane  in  front  of  V  be  revolved  to  the  right,  a"  comes 
into  the  new  position  a",  a  distance  to  the  right  of  Ga  La 
equal  to  Aa'  and  a  distance  above  G  L  equal  to  Aa,  or  on 
the  horizontal  line  thru  a'. 

Projections  of  objects.  Advancing  from  the  point  A 
just  discussed,  to  all  other  elemental  points  of  the  object 
and  projecting  them  in  turn  in  the  same  manner  as  was  A, 


Fig.   7 

we  find  the  representation  of  the  machine  part  in  the 
first  angle,  when  the  several  points  are  properly  joined  by 
lines,  to  be  as  shown  in  Fig.  5.  Proceeding  in  the  same 
manner  with  the  object  in  the  third  angle  we  obtain  the 
views  as  shown  in  Figs.  6  and  7.  It  should  be  noted  that 


ORTHOGRAPHIC  PROJECTION 


t_i_  __i__i 
!     I  1 


Fig.   8 


the  views  are  identical  in  character  but  appear  in  differ- 
ent positions  in  respect  to  each  other.    In  practice  it  is 
the  universal  custom  to  omit 
both  ground  lines  together 
with  the  boundary  lines 
of   the    three    planes.     The 
resulting  projections  of 
the    object    appear    as    in 
Fig.  8. 

Elimination  of  the  first 
angle.  From  Fig.  1,  it  is 
noted  that  as  we  ordinarily 
see  objects  the  top  appears 

above  the  front  and  the  right  end  to  the  right  of  the 
front  or  the  left  end  to  the  left  of  the  front,  according  to 
the  position  from  which  the  object  is  seen.  When  the 
object  is  placed  in  the  first  angle  and  the  projections 
revolved  into  the  positions  shown  in  Fig.  5,  it  is  seen 
that  the  left  end  projection  comes  in  a  position  to  the 
right  of  the  front  and  that  the  top  is  under  the  front, 
an  arrangement  by  no  means  natural.  While,  when  the 
object  is  placed  in  the  third  angle,  Fig.  6,  and  projections 
revolved  as  shown  in  Fig.  7,  the  views  assume  a  group- 
ing identical  with  their  order  on  the  object  itself;  i.e., 
the  right  end  to  the  right  of  the  front,  and  the  top  above 
the  front.  Merely  for  the  sake  of  this  natural  arrange- 
ment the  third  angle  will  be  selected  in  preference  to  the 
first  in  making  working  drawings;  i.  e.,  all  working  draw- 
ings will  be  third  angle  orthographic  projections. 


60  MECHANICAL  DRAFTING. 

SUMMARY   OF  PRINCIPLES 

(33)  It  may  be  well  to  summarize  a  number  of  prin- 
ciples brought  out  in  this  discussion,  likewise  to  mention 
several  violations  of  pure  orthographic  projection.    The 
top  view,  Fig.  8,  represents  the  exact  appearance,  with 
lines  in  true  proportions,  of  the  top  of  the  object;  the 
front  vieiv  represents  the  same  of  the  front  of  the  object, 
and  the  side  view  the  same  of  the  side  of  the  object. 

The  top  and  front  views  must  be  directly  above  and 
below  each  other  and  the  front  and  end  views  must  be 
on  the  same  horizontal  lines  as  shown  in  Fig.  7,  if  the 
group  is  to  represent  the  true  orthographic  projection 
of  the  object;  a  violation  of  this  renders  the  whole  draw- 
ing incorrect. 

PERMISSIBLE  VIOLATIONS 

(34)  In  Fig.  5,  it  is  shown  that  the  portion  of  the 
End  or  Profile  plane  in  front  of  V  is  revolved  to  the  right; 
this  of  course  means  that  the  portion  of  the  Profile  plane 
behind  V  revolves  to  the  left;  while,  in  Fig.  7,  the  portion 
of  the  Profile  plane  behind  V  is  represented  as  being  re- 
volved to  the  right.    This  revolution  to  the  right  of  the 
portion  of  the  Profile  plane  behind  V  is  ortho graphically 
incorrect;  however,  in  the  case  of  the  third  angle  projec- 
tions it  is  tolerated  for  the  natural  order  of  projections 
which  it  produces. 

PROJECTIONS  OF  HIDDEN  LINES 

(35)  In  Figs.  5  and  7  certain  lines  of  the  projections 
are  shown  dotted  lines.    This  is  the  custom  always  fol- 
lowed for  showing  hidden  or  invisible  lines.     For  ex- 
ample in  the  projection  on  the  V  plane,  the  two  dotted 


ORTHOGRAPHIC  PROJECTION 


61 


lines  show  that  the  hole  thru  the  object  is  invisible  when 
viewed  in  a  direction  perpendicular  to  the  V  plane.  A 
simple  rule  for  determining  the  visibility  of  a  line  is  to 
always  consider  the  H  projection  a  view  from  the  top 
and  the  V  projection  a  view  from  the  front.  This  ap- 
plies equally  to  first  and  third  angle  projection.  The 


Fig.   10 


projection  on  the  P  plane  is  considered  a  view  from  the 
corresponding  side  of  the  object,  that  is,  looking  perpen- 
dicularly thru  the  P  plane  at  the  object. 


AUXILIARY  PLANES  OF  PROJECTION 

(36)  Frequently  an  object  is  so  shaped  that  it  can- 
not be  placed  in  an  entirely  simple  position  with  respect 
to  the  planes  of  projection.  The  face  K  on  the  corner 
brace  shown  in  Fig.  9  will  not  be  shown  in  its  true  size 


62 


MECHANICAL  DRAFTING. 


on  either  the  H,  V,  or  P  planes  when  the  object  is  placed 
in  its  simplest  position  with  respect  to  these  planes. 


Fig.  11 


The  use  of  a  fourth  plane,  which  is  perpendicular  to  H 
but  parallel  to  face  K,  will  give  an  additional  view  which 
will  show  K  in  its  true  size.  Fig.  10. 

Fig.  11  shows  the  correct  arrangement  of  the  four 
views  of  the  object  after  the  V,  P,  and  auxiliary  planes 
have  been  revolved  into  the  H  plane. 


ORTHOGRAPHIC  PROJECTION 


POSITIONS  OF  THE  THIRD  AND  FOURTH  VIEWS 
OF  AN  OBJECT 

(37)  In  Fig.  12  is  shown  the  correct  arrangement, 
orthographically,  of  the  three  views  of  an  object-box. 
However,  occasions  may  arise  in  which  it  will  be  in- 


Fig.   12 


convenient  to  place  the  side  view  directly  opposite  the 
front;  in  this  case  we  may  imagine  that  the  line  of  inter- 
section of  the  end  plane  and  the  horizontal  plane  becomes 
an  axis  about  which  the  end  plane  is  revolved,  Fig.  13, 
until  it  coincides  with  the  horizontal  plane.  This  entire 
horizontal  plane  is  then  revolved  about  its  line  of  inter- 
section with  V  as  an  axis,  until  it  coincides  with  V.  The 
side  view  will  now  be  found  opposite  the  top  instead  of 
the  front.  If  two  side  views  are  necessary  to  show  the 
construction  they  may  be  placed  on  either  side  of  the 


MECHANICAL  DRAFTING. 


front  view,  Fig.  14,  or  on  either  side  of  the  top  view, 
Fig.  15.    No  other  arrangement  is  permissible. 


Fig.   14 

In  constructing  a  three  view  drawing  it  is  best  always 
to  construct  the  top  and  front  views  from  dimensions 
and  by  projection; 
then,   to   obtain   the 
side  views  from  these 
two,  entirely  by  con- 
struction and  not  by 
the  use  of  dimensions. 
For  the  sake  of  con- 
struction   the     two 
ground  lines,  Fig.  12, 
may    be    drawn    in 
lightly;  however,  they  should  be  erased  when  no  longer 
needed. 


Fig.   15 


WORKING  DRAWINGS. 


65 


CHAPTER  4 

WORKING  DRAWINGS 
WORKING  DRAWING 

(38)  Definition.  A  working  drawing  of  a  piece  of 
machinery  is  such  a  group  of  correctly  and  completely 
dimensioned  orthographic  views  of  that  object  as  will 
give  all  the  information  necessary  in  constructing  a 
duplicate  of  the  same.  Fig.  1. 


* 

I  Ka* 

H 

L± 

E 

^zzzzZi^zfiii: 

1-1  — 
i    i 

Sr 

T    L                   1             1 

Fig.  1 


DETAIL  DRAWING 

(39)  Definition.  A  detail  drawing  is  a  working 
drawing  of  one  piece  of  any  machine. 

A  group  of  detail  drawings  of  all  of  the  parts  of  a 
machine  or  any  collection  of  parts  is  termed  a  set  of 
details. 


66  MECHANICAL  DRAFTING. 

ASSEMBLY  DRAWING 

(40)  Definition.    An  assembly  drawing  of  a  machine 
is  a  one,  two  or  three  view  orthographic  projection  of  a 
machine  completely  assembled;  i.  e.,  all  parts  in  their 
proper  working  place.    Figs.  2. 

Uses.  Assembly  drawings  have  three  important  uses. 
(1)  As  an  index  to  a  working  drawing;  i.  e.,  an  assembly 
of  a  machine  is  ordinarily  given  with  the  set  of  detail 
working  drawings  to  explain  the  use  of  each  of  these  de- 
tails in  the  machine;  (2)  For  purposes  of  advertisement 
or  magazine  illustration;  (3)  As  a  construction  guide  in 
assembling  machines  which  may  be  sent  out  from  shops 
in  sections. 

Characteristics.  Some  characteristics  which  may  be 
noted  of  assembly  drawings  when  used  for  any  of  the 
above  purposes  are:  (a)  All  dimensions  are  ordinarily 
omitted;  (b)  The  several  views  are  elaborately  sectioned 
to  explain  clearly  all  inside  constructions;  (c)  When 
given  with  a  set  of  details  the  assembly  will  ordinarily 
occupy  a  fixed  relative  place  on  the  sheet,  i.  e.,  the  lower 
left  corner  or  whole  left  side  if  necessary. 

DETAIL  WORKING  DRAWINGS 

(41)  Arrangement  of  set  of  details.    In  making  a  set 
of  details  a  certain  order  of  arrangement  should  be  fol- 
lowed, both  for  appearances  and  ease  in  reading  the  draw- 
ing.   As  mentioned  under  assembly  drawings,  the  assem- 
bly should  occupy  the  left  portion  of  the  sheet.    In  gen- 
eral, the  arrangement  of  the  details  on  the  sheet  should 
be  such  as  to  suggest  their  direct  relation  in  the  machine 
itself;  i.  e.,  such  an  arrangement  as  is  suggested  by  the 
relation  of  these  parts  in  the  assembly.  It  may  not  always 


WORKING  DRAWINGS. 


67 


Fig.  2 


MECHANICAL  DRAFTING. 


WORKING  DRAWINGS. 


69 


70 


MECHANICAL  DRAFTING. 


WORKING  DRAWINGS. 


71 


be  possible  to  carry  out  this  scheme 
completely;  however,  in  general  it 
will  be  found  possible  so  to  arrange 
the  main  details.  For  further  ex- 
planation see  Fig.  3.  The  assembly 
is  here  shown  to  the  left,  followed 
along  the  bottom  of  the  sheet  by  the 
main  detail,  the  remaining  details 
being  arranged  about  the  sheet 
properly  with  relation  to  each  other 
if  not  to  the  main  details.  Fig.  3a 
shows  an  arrangement  with  the  as- 
sembly omitted. 


Fig.  4 


r 


Fig.  5 


72 


MECHANICAL  DRAFTING. 


Order  of  work  in  a  set  of  details.    In  making  a  set  of 
details,  e.  g.,  of  the  bell  crank,  Fig.  4,  the  following  order 


Fig.   6 

of  work  will  be  found  to  lend  to  the  greatest  speed: 
(a)  Make  list  of  details  to  be  drawn  and  number  of  views 
required  of  each,  (b)  Select  scale,  (c)  Draw  on 
pieces  of  scrap  paper  rectangles  or  rectangular  figures 
of  the  proper  size  to  enclose  the  desired  number  of 
views  of  each  detail.  '  (d)  Cut  out  these  rectangles 
and  arrange  them  on  the  sheet  of  drawing  paper  on 
which  the  details  are  to  be  drawn,  (e)  After  the 
rectangles  are  arranged  mark  their  positions,  Fig.  5. 
(f )  Divide  the  rectangles  on  the  sheet  of  drawing  paper 
into  smaller  rectangles  to  contain  the  separate  views  of 
each  detail,  Fig.  6.  The  rectangles  mentioned  in  (e) 


WORKING  DRAWINGS. 


and  (f)   should,  of  course,  be  put  in  only  lightly  and 
may  be  erased  when  no  longer  needed.    Fig.  7. 


Fig.   7 


Detail  signature.  Accompanying  each  detail  draw- 
ing, whether  the  detail  drawing  be  by  itself  or  one  of  a 
set,  should  be  given  a  characteristic  signature  containing 
the  following  information:  Name  of  the  machine  part, 
material  of  which  it  is  made,  number  of  parts  required, 
and  some  arbitrary  number  for  the  pattern  if  the  object 

Valve  Crank— C.  I. 

Reqd—  1. 
Pattern  No.  A-3. 

is  to  be  cast.    This  information  should  be  given  in  the 
manner  shown  above. 


74 


MECHANICAL  DRAFTING. 


The  letter  A  in  the  pattern  number  refers  to  the  sheet 
A  of  the  Details  of  the  Corliss  engine  of  which  this  valve 
crank  is  a  part ;  the  number  A-3,  indicates  that  the  valve 
crank  is  detail  number  3  on  sheet  A. 

ORDER  OF  PENCIL  WORK 

(42)  The  most  rapid  progress  can  be  gained  in  the 
pencil  work  of  a  working  drawing  by  following  the  order 
given  in  Fig.  8. 

Caution.  It  is  by  no 
means  wise  to  attempt  to  fin- 
ish one  of  several  views  be- 
fore doing  any  work  on  the 
others.  Fewer  mistakes  will 
be  made  and  more  rapid 
progress  gained  by  working 
on  all  views  at  the  same 
time;  i.e.,  when  a  line  is 
placed  on  one  view,  its  pro- 
jections in  the  other  views  should  be  obtained  before 
proceeding  with  other  lines.  All  views  will  thus  be  fin- 
ished at  practically  the  same  time.  When  one  projection 
of  a  line  is  obtained  from  a  given  dimension,  the  other 
views  of  this  same  line  should  be  obtained  by  the  prin- 
ciple of  projection  rather  than  by  making  use  of  the 
scale  a  second  time.  This  practise,  tho  it  may  permit  a 
mistake  to  remain  undetected,  has  the  advantage  of  pro- 
ducing drawings  which  are  true  orthographic  projections. 


Pig.   8 


WORKING  DRAWINGS.  75 

ORDER  OF  PENCIL  WORK 

1 — Border  Lines 

2— Title  Space 

3— Selection  of  Scale 

4 — View  Spaces 

5 — Center  Lines 

6 — Outlines 

7 — Auxiliary  and  Dimension  Lines,  and  Dimensions 

8 — Section  Lines  and  Notes 

DIMENSIONING 

(43)     In  dimensioning  the  following  rules  or  sugges- 
tions should  be  observed : 

(a)  Dimensions  should  read  from  left  to  right  or 
up,  and  in  the  direction  of  the  dimension  line.    Fig.  9. 

(b)  The  auxiliary  lines  used  in  dimensioning  should 
not  quite  connect  with  the  lines  from  which  they  lead. 
Fig.  10. 

(c)  Series.    A  series  of  dimensions  should  be  given 
on  one  continuous  dimension  line,  as  in  Fig.  11,  and  not 
as  in  Fig.  12. 

(d)  An  overall  dimension  should  always  accompany 
a  series,  both  as  a  check  and  for  the  convenience  of  the 
workman.    Fig.  11. 

(e)  Diameters.    Diameters  should  be  placed  on  a 
linear  diameter  of  the  circle  as  in  Fig.  13  whenever 
possible;  when  necessary  to  indicate  the  diameter  on  a 
straight  line  projection  of  a  circle,  the  dimension  should 
be  accompanied  by  the  letter  D. 

(f )  Eadii  of  arcs  should  be  marked  R.    Fig.  14. 


76 


MECHANICAL  DRAFTING. 


Fig.  15 


Pig.  16 


WORKING  DRAWINGS.  77 

(g)  Inasmuch  as  the  meaning  of  hidden  lines  is  not 
always  clear,  it  is  bad  practice  to  place  dimensions  on 
such  lines. 

(h)  Place  dimensions  between  views  unless  clear- 
ness will  be  gained  by  placing  them  otherwise. 

(i)     Do  not  repeat  dimensions  on  adjacent  views. 

(j)     Dimensions  should  not  be  crowded. 

(k)  Dimensions  always  indicate  the  size  of  the  fin- 
ished object. 

(1)  Do  not  place  dimensions  on  or  along  Center 
Lines.  Fig.  15. 

Jm)  In  general  dimension  from  the  center  lines  and 
not  from  the  outlines  of  the  object. 

(n)  Fractions  should  be  made  with  a  dividing  line 
in  the  same  line  with,  but  not  a  part  of  the  dimension 
line.  Fig.  11. 

(o)  The  arrows  of  dimension  lines  contain  two 
barbs,  while  those  of  leaders,  Figs.  13  and  16,  but  one. 

(p)  Arrows  should  be  so  placed  that  there  may  be  no 
confusion  as  to  which  line  they  point  to. 

(q)  Leaders,  All  leaders,  Fig.  16,  should  be  made 
mechanically  and  not  freehand. 

(r)  Notes.  For  explanatory  notes  the  leader  should 
end  so  that  the  notes  may  read  either  horizontally  or 
vertically  as  the  dimensions,  but  not  diagonally.  Fig.  16. 

(s)  Dimensions  up  to  two  feet  should  be  stated  in 
inches;  e.  g.,  12",  18",  etc. 

Two  feet  may  be  written  either  as  24"  or  2'-0". 

Except  for  sheet  metal,  dimensions  above  two  feet 
should  be  expressed  as  follows :  2'-3",  6'-4",  7'-0",  etc. 

The  dimensions  for  sheet  metal  should  be  given  in 
inches  and  in  the  order  of  thickness,  width,  length; 


78 


MECHANICAL  DRAFTING. 


WORKING  DRAWINGS.  79 

SECTIONING 

(44)  The  primary  function  of  orthographic  projec- 
tion is,  of  course,  to  represent  the  portions  of  an  object 
visible  to  the  eye.  Any  constructions  hidden  by  the  sur- 
faces in  view  may  be  represented  by  conventional  lines 
known  as  hidden  lines,  Fig.  17.  The  dotted  lines  in  this 
figure  represent  the  three  recesses  in  the  top,  front,  and 
side  of  the  cube.  It  may  be  satisfactory  to  represent  in 
this  way  the  interior  construction  of  so  simple  an  affair 
as  the  object  shown;  however,  if  the  interior  construction 
is  in  the  least  elaborate  this  method  is  by  no  means  satis- 
factory. If  an  interior  construction  be  represented  by  a 
number  of  hidden  lines  which  cross  each  other,  the  draw- 
ing becomes  so  vague  as  to  be  almost  unintelligible.  For 
this  reason  a  substitute  method  has  been  devised  for 
showing  any  interior  or  hidden  construction.  According 
to  this  method  it  may  at  any  time  be  imagined  that  a 
cutting  plane,  parallel  to  one  of  the  coordinate  planes, 
can  be  drawn  in  any  position,  cutting  away  such  portions 
of  the  object  as  will  expose  any  other  parts  one  may  wish 
to  see.  Ordinarily  these  planes  will  be  found  to  pass  thru 
some  axial  line  of  the  object,  Fig.  18 ;  however,  if  desired, 
they  may  be  imagined  drawn  elsewhere,  Fig.  19.  This 
process  of  sectioning  is  purely  imaginary  and  may  be 
represented  on  only  one  view  of  a  two  or  three  view 
working  drawing,  the  other  views  representing  the  ob- 
ject unsectioned  by  any  such  plane.  The  process  of  sec- 
tioning is  strictly  utilitarian ;  i.e.,  one  should  section  only 
objects  whose  construction  can  be  more  clearly  explained 
by  this  process  than  otherwise. 

Certain  terms  applying  to  sections  are  sometimes 
confused  from  the  fact  that  they  may  apply  either  to  the 


80 


MECHANICAL  DRAFTING. 


drawing  or  the  object.    These  terms  are  quarter  section, 
half  section,  and  full  section.    The  confusion  ordinarily 
comes  between  the  terms  quarter  and  half  section.  From 
Fig.  20,  it  is  seen  that  when  one-quarter  of  the  object  is 
removed  one-half  of  the  drawing  will  be  found  sectioned. 
Likewise  if  the  entire  front  or 
half  of  the  object  were  removed 
the  drawing  would  be  full  sec- 
tioned.   Hence  the  term  quarter 
section  will  then,  of  course,  be 
entirely  discarded,  as  it  can  refer 
only  to  the  object. 

Solid  cylinders.  The  drafts- 
man should  keep  in  mind  the  fact 
that  there  is  but  one  thing  to  be 
gained  in  sectioning,  i.  e.,  to  show 
more  clearly  the  interior  construc- 
tion of  any  piece  of  machinery; 
if  the  section  does  not  accomplish 
this  purpose  it  is  just  so  much 
wasted  labor.  This  point  refers 
particularly  to  solid  cylinders, 
e.  g.,  shafts,  Fig.  21,  bolts,  screws, 
etc.,  which  should  never  be  sec- 
tioned. 


Fig.   21 


Interpolated  or  Revolved  Sections.  In  such  cases 
as  are  shown  in  Fig.  22,  with  respect  to  rims  and  spokes 
of  wheels,  standard  construction  iron,  etc.,  sections  known 
as  interpolated  or  revolved  sections  are  given  to  show 
the  cross-section  of  the  material  at  certain  places.  These 
sections  are  obtained  by  passing  planes  perpendicular 


WORKING  DRAWINGS. 


to  the  axis  of  the  piece  to  be  sectioned  and  revolving 
this  plane  90°  about  the  center  line  of  the  section  thus  cut. 


Fig.  22 


Section  thru  spokes.  Whenever  the  cutting  plane 
passes  thru  spokes  of  wheels  as  is  the  case  shown  in 
Fig.  22,  the  cross  hatching  is  put  in  as  if  the  plane  had 
been  passed  on  the  line  AB. 

Section  lines.  Indication  of  material  by  variation  in 
section  lines.  It  is  the  custom  in  many  shops  to  indicate 
the  material  of  which  a  piece  of  machinery  is  to  be  made 
by  using  a  characteristic  section  line  for  any  parts  of 
that  piece  which  have  been  sectioned,  Fig.  23.  There 
are  some  apparent  disadvantages  in  this,  however,  for 
there  is  at  present  no  universal  standard  system  of  sec- 
tion lining.  Some  shops  use  one  characteristic  for  brass, 
wrought  iron,  etc.,  and  others  a  radically  different  char- 
acteristic. Furthermore,  unless  one  uses  these  section 


82 


MECHANICAL  DRAFTING. 


Fig.  23 


lines  constantly  or  has  a  chart  of  them  with  him  always, 
he  may  find  it  quite 
difficult  to  remem- 
ber some  of  them. 
A  third  objection 
is  that  it  requires 
an  excessive 
amount  of  time  to 
draw  some  of  these 
section  lines. 

Indication  of  materials  by  abbreviations  and  univer- 
sal section  lines.  For  greatest  convenience  and  ease, 
both  in  making  and  reading  a  drawing,  the  writers 
approve  the  universal  section  lining  with  material  abbre- 
viations as  a  sub- 
stitute for  the 
above  system,  i.  e., 
the  use  of  the 
standard  section 
line  now  used  for 
cast  iron  as  the 
standard  for  all 
materials  and  the 
particular  material 
of  which  the  piece 
is  to  be  made  indi- 
cated' by  its  char- 
acteristic abbrevia- 
tion as  shown  in 
Fig.  24.  These  ab- 
breviations are 

easy  to  remember  and  the  section  lines  can  be  drawn 
rapidly. 


Where  necessary  a  variation  in  space 
between  section  lines  may  be  substituted 
for  a  change  in  direction  of  lines 

Fig.  24 


WORKING  DRAWINGS.  83 

TRACING 

(45)  Tracing  cloth  is  a  fine  quality  of  cotton  coated 
with  a  preparation  which  gives  it  a  smooth  hard  surface 
and  renders  it  transparent.  Of  the  various  grades  of 
cloth  on  the  market,  the  imported  brand  "Imperial" 
gives  by  far  the  greatest  satisfaction  and  is  recom- 
mended for  general  use.  Always  before  making  use  of 
any  piece  of  cloth  be  sure  to  rip  off  about  ys"  of  the 
selvage  edge;  it  may  prevent  a  bad  buckling  of  the 
tracing. 

Tacking  to  the  board.  It  is 
best  always  to  have  the  sheet 
of  tracing  cloth  slightly  larger 
than  the  sheet  of  paper  so  that 
the  tacks  used  in  pinning  down 
the  cloth  may  be  placed  outside 
the  sheet.  In  tacking  down  the 
cloth,  preferably  with  the  dull 
side  up,  be  sure  to  stretch  very  rig  25 

tight  and  tack  firmly.    See  Fig. 
25  for  best  order  of  tacking. 

Preparation  of  the  surface  of  the  cloth.  Unless  pre- 
pared in  some  way,  the  surface  of  the  tracing  cloth  will 
likely  take  the  ink  very  poorly,  giving  ragged  and  faded 
out  lines.  The  cloth  may  be  dusted  or  rubbed  with  chalk 
or  preferably  magnesium  carbonate,  which  may  be  pur- 
chased at  any  drug  store  in  5-cent  blocks,  and  then  rubbed 
with  a  piece  of  linen. 

Order  of  work.  Unless  one  is  sure  of  being  able  to 
finish  the  tracing  of  several  views  of  a  drawing  before  it 


84  MECHANICAL  DRAFTING. 

is  necessary  to  stop  work,  it  will  be  found  best  always  to 
trace  one  view  at  a  time,  finishing  that  view  before  leav- 
ing work.  Tracing  cloth  has  a  decided  tendency  to 
stretch  and  warp,  and  it  may  be  found  most  difficult  to 
make  old  lines  check  with  new  if  the  tracing  has  been  left 
standing  for  a  day  or  more. 

Erasing.  In  erasing,  use  the  pencil  eraser  always  in 
preference  to  the  ink  eraser  or  knife.  It  may  require 
more  time  to  erase  a  mistake; 
however,  the  cloth  will  be 

found  in  good  condition  after       

such  erasing ;  while  the  ink  era-      


Scrape  out 
/with  knitV 


ser  or  knife  quite  easily  rough- 
ens the  surface  and  causes  blots  on  application  of  new 
ink.    A  knife  may  be  used  to  advantage  in  scraping  out 
slight  accidental  extensions  of  lines,  Fig.  26. 

Caution.  If  necessary  to  rule  across  ink  lines,  be 
sure  to  move  the  pen  rapidly.  If  the  pen  is  moving 
slowly  the  ink  will  likely  follow  down  the  old  ink  line  to 
the  T-square  or  triangle  and  cause  a  bad  blot. 

Weights  of  lines.  The  visible  and  hidden  outlines  are 
the  heaviest  lines  on  the  drawing  and  should  be  slightly 
less  than  1/32"  in  width.  This  weight  may  be  obtained 
by  using  a  number  3  line  on  the  adjustable  graduated 
detail  pen.  All  other  lines  on  the  drawing,  i.e.,  dimen- 
sion, auxiliary,  center,  and  section  lines,  should  have  a 
weight  of  number  one.  Fig.  27. 

Order  of  inking  in  tracing.  In  tracing,  the  following 
order  should  be  observed  for  most  rapid  and  accurate 
work. 


WORKING  DRAWINGS.  85 

Visible  Outline 


Hidden  Outlines 


Dimension,  Auxiliary  and  Section  Lines 


Fig.  27 


Undercut  Tracing  Ruler 


Fig.  28 

1.  Center  lines. 

2.  Large  circles  and  arcs. 

3.  Small  circles  and  arcs  with  the  bow  pen. 

4.  Irregular  curves  with  special  curve. 

5.  Horizontal  lines  with  the  T-square. 

6.  Vertical  lines  with  T-square  and  triangles. 

7.  Inclined  lines  in  groups,  e.  g.,  30°,  45°,  and  60°. 

8.  Other  oblique  lines. 

9.  Dimension  and  auxiliary  lines. 

10.     Section  lining,  dimensions  and  notes. 

BEVELLED  AND  RAISED  TRACING  RULES 

(46)  For  tracing,  the  two  rulers  shown  in  Figs.  28 
and  29  are  indispensable.  With  the  bevelled  ruler,  Fig. 
28,  it  is  possible  to  rule  across  inked  lines  without  any 
danger  of  blotting.  The  raised  ruler  of  Fig.  29  saves  an 


86 


MECHANICAL  DRAFTING. 


6  inch  section  from  18  inch  beveled  celluloid 
ruler  sold  by  Frederick  Post  Company.  Screw 
the  point  thru  one-eight  inch.  Cut  off  on  top 
and  file  smooth. 


Fig.  29 

immense  amount  of  time,  as  it  makes  it  possible  to  con- 
tinue tracing  no  matter  how  many  ink  lines  are  still  wet. 

CONVENTIONAL  LINES 

(47)  The  conventional  lines  shown  in  Fig.  27  are 
standard  and  should  be  followed  strictly.     Concerning 
the  hidden  lines,  it  may  be  said  that  no  one  thing  except 
dimensions  will  add  to  or  detract  from  the  appearance  of 
a  drawing  more  than  care  or  lack  of  it  in  the  correct  draw- 
ing of  hidden  lines,  both  as  to  the  uniform  length  of  the 
dashes  and  uniform  space  between  dashes.    In  tracing, 
follow  strictly  the  weights  given  in  the  figure  for  these 
various  conventional  lines. 

SCALES 

(48)  Architect's   scale.     The   spaces   representing 
feet  on  the  architect's  scale  are  divided  into  twelve  equal 
parts,  making  it  possible  to  draw,  without  any  interpo- 


WORKING  DRAWINGS.  87 

lation,  plans,  etc.,  of  objects  whose  dimensions  are  given 
in  feet  and  inches. 

Engineer's  scale.  On  the  engineer's  scale  the  inches 
are  divided  into  various  numbers  of  subdivisions,  these 
numbers  being  multiples  of  ten;  i.  e.,  the  inches  are 
divided  into  10,  20,  30,  40,  50,  or  60  divisions.  By  use  of 
this  scale  without  any  interpolation  maps  may  be  made 
and  drawings  plotted  directly  from  field  notes  in  which 
the  distances  are  all  given  in  feet  and  tenths  of  feet. 

Mechanical  engineer's  scale.  Recently  a  scale  has 
been  placed  on  the  market  on  which  the  spaces  repre- 
senting inches  have  been  divided  into  halves,  quarters, 
eighths,  sixteenths,  etc.  Likewise  a  scale  that  combines 
all  of  the  three  scales  just  described.  Mechanical  engi- 
neers will  find  it  to  their  advantage  to  own  one  or  both 
of  these. 

Scale  versus  size.  A  drawing  made  to  such  a  size 
that  one-half  inch  on  the  drawing  equals  one  foot  on  the 
object  drawn,  is  said  to  be  made  to  one-half  scale.  How- 
ever, if  the  drawing  be  made  so  that  one-half  inch  on  the 
drawing  represents  one  inch  on  the  object  the  drawing  is 
said  to  be  made  one-half  size  or  to  a  scale  of  "  to  V. 


MECHANICAL  DRAFTING. 

CHAPTER  5 

FASTENERS 

(49)  In  every  field  of  construction  the  builder  finds 
it  necessary  to  hold  the  component  parts  of  the  whole 
together  by  means  of  fasteners.    Among  the  numerous 
kinds  and  varied  shapes  of  fasteners,  several  are  of  such 
universal  importance  that  the  draftsman  as  well  as  the 
mechanic  must  be  entirely  familiar  with  the  method  of 
manufacture  and  manner  of  representing  them  on  draw- 
ings. 

Among  others,  rivets,  keys,  bolts  and  screws  are  to  be 
specially  noted.  The  several  kinds  of  rivets  with  their 
customary  conventional  representations  will  be  found  in 
the  appendix.  Brief  mention  is  made  of  the  common 
standard  keys  in  Art.  59.  The  greater  portion  of  this 
chapter  will  be  devoted  in  main  to  the  most  widely  used 
fasteners,  Bolts  and  Screws. 

THREADS 

(50)  The  Helix.    The  helix  is  a  mathematical  curve 
often  wrongly  termed  the  Spiral.    It  is  generated  by  mov- 
ing a  point  on  any  surface  of  revolution,  around  and 
along    the    axis    of    revolution.      The    motion    of    the 
point  in  both  directions  is  generally  uniform  but  may  be 
variable  in  either  or  both  of  its  motions.    Thus  we  may 
have  cylindrical,  conical,  spherical  and  many  other  forms 
of  helices.     On  Bolts  and  Screws  the  thread  is  almost 
always  a  cylindrical  helix.     For  special  purposes  the 


FASTENERS. 


thread  may  be  a  conical  helix.     The  threads  on  water 
pipes  and  their  connections  are  of  this  class.     Fig.  1 
shows  the  geometric  method  of  constructing  a  cylindrical 
helix,  which  form  will  always  be 
understood  when  the  term  Helix 
is    used.      The    distance    (x)    is 
called  the  pitch  of  the  helix  and 
may  be  assumed  at  will.    In  con- 
structing the  helix  the  pitch  dis- 
tance is  divided  into  the  same 
number  of  axial  divisions  as  is 
the  projected  circle. 

From  a  mathematical  stand- 
point, a  thread  is  simply  a  helix 
cut  around  and  into  a  solid  cone 
or  cylinder. 

THREADS  CLASSIFIED 

(51)  V  and  Square  threads. 
Threads  may  be  divided  into  two 
general  types  or  groups,  called  V 
threads  or  Square  threads  accord- 
ing to  the  shape  of  the  tool  used 
in  cutting  them.  Each  of  these 
groups  may  be  further  classified 
as  Single,  Double,  Triple  threads, 

etc.  This  latter  classification  depends  upon  the  number 
of  separate  threads  that  are  turned  on  one  bar  of  metal. 
All  threads  are  in  general  Single  threads  except  in  cases 
where  rapidity  of  motion  is  required  without  a  corre- 
sponding increase  in  coarseness  of  thread.  Some  ex- 


Fig.  3 


90 


MECHANICAL  DRAFTING. 


amples  of  the  foregoing  mentioned  threads  are  shown 
in  Fig.  2. 


Single 


V  Threads.  The  V  thread  is  the  usual  thread  found 
on  bolts  and  screws.  It  derives  its  name  from  the  re- 
semblance of  its  profile  to  the  letter  V.  There  have  been 
devised  numerous  modifications  of  this  thread  intended 
to  make  it  stronger  and  more  durable  and  in  some  in- 
stances to  fit  special  classes  of  work.  Fig.  3  shows  the 
profiles  of  some  of  these  modified  V  threads.  Of  these 


FASTENERS. 


91 


several  types  the  U.  S.  Standard  (Seller's)  thread  is  the 
most  used  in  this  country.  Sizes  and  dimensions  for  this 
class  of  threads  will  be  found  in  the  Appendix. 


Sharp  V 


U.  S.  Standard 


Fig.  3 


Square  threads.    In  cases  where  a  thread  is  con- 
stantly being  drawn  or  loosed  or  where  heavy  loads  are 


Square 


B  &  S  Worm  Thread 


Fig.  4 


to  be  lifted,  the  square  thread  finds  an  important  place 
due  to  the  reduced  friction  over  the  V  thread.     This 


92  MECHANICAL  DRAFTING. 

thread  finds  a  further  field  of  usefulness  in  transmitting 
motion.  As  with  the  V  thread,  many  modified  forms 
have  been  devised.  Fig.  4  illustrates  a  few  of  these 
forms. 

DEFINITION  OF  THREAD  TERMS 

(52)  Crest,  Root.  The  sharp  edge 
of  the  thread  is  known  as  the  crest; 
the  depression  line  as  the  root,  Fig.  5. 
The  term  crest  or  outside  diameter 
is  used  to  denote  the  diameter  of  the 
crest  of  the  thread  and  is  assumed 
equal  to  the  diameter  of  the  bar.  The 
diameter  of  the  bottom  of  the  grooves 
is  known  as  the  root  diameter  and  is 
approximately  equal  to  the  crest  di- 
ameter of  the  nut  or  the  diameter  of 
tap  drill. 

Pitch.  For  bolts  and  screws  of 
various  diameters  the  size  of  the 
threads  must  vary,  hence  the  number 
of  threads  per  linear  inch  must  vary.  For  each  size  bolt 
or  screw  there  is  a  standard  number  of  threads  per  linear 
inch  which  is  often  improperly  termed  the  pitch  of  the 
thread.  The  distance  B,  shown  in  Fig.  5,  denotes  the 
pitch  of  the  thread  on  the  bolt.  It  should  always  be 
understood  that  when  the  term  pitch  is  used  the  distance 
between  two  adjacent  threads  is  meant,  whether  the 
thread  is  single,  double,  or  triple.  In  the  case  of  the  latter 
two  threads  the  term  lead  is  used  to  denote  the  distance 
between  crests  on  the  same  helix. 


FASTENERS. 


93 


CONVENTIONAL  REPRESENTATION  OF  THREADS 

(53)  As  noted  above,  the  projections  of  threads  on 
planes  parallel  to  the  axis  of  the  threads  are  curved  lines. 
As  each  thread  requires  two 
helices  for  its  complete  projec- 
tion— root  and  crest,  Fig.  2 — 
standard  conventions  have  been 
evolved  to  represent  the  differ- 
ent threads.  On  large  threads 
the  curved  lines  are  replaced 
by  straight  lines;  the  projec- 
tion of  the  thread  remaining 
otherwise  the  same.  Examples 


Single 


Single 


Single 


Fig.   6 


Pig.   7 


of  these  conventions  are  shown  in  Fig.  6. 

On  threads  one  inch  or  less  in  diameter  the  profiles  are 
omitted  altogether  and  the  forms  shown  in  Fig.  7,  A,  B 
and  C  are  used.  In  drawing  these  conventions  care  must 
be  used  not  to  make  the  slope  of  the  lines  too  great,  one- 
half  the  pitch  being  right.  The  spacing  may  be  done  by 
eye  but  should  conform  in  a  relative  way  to  the  number  of 
threads  on  the  several  bolts  or  screws  on  a  drawing. 


MECHANICAL  DRAFTING. 


Light  pencil  guide  lines  should  be  ruled  limiting  the 
length  of  the  short  heavy  lines  which  should  be  equal  to 
the  root  diameter  of  the  thread.  When  threads  are  to 
be  shown  as  invisible  lines,  the  convention  as  shown  in 


•   Tapped  Hole  in  Section 
Pig.  8 

A  Fig.  8  is  recommended.  Altho  possessing  no  appear- 
ance of  a  thread  it  is  easy  to  construct  and  is  universally 
understood  by  mechanics.  Fig.  8  represents  the  conven- 
tional way  of  showing  threads  in  tapped  holes,  the  largest 
diameter  being  known  as  the  diameter  of  the  thread. 
In  some  instances  threads  may  be  made  left  handed. 


FASTENERS. 


95 


Care  should  be  taken  to  show  such  threads  by  the  proper 
slope  of  the  lines.  Also  attention  is  directed  to  the 
change  in  direction  of  slope  for  threads  in  sectioned  parts. 
These  variations  may  be  understood  more  fully  by  ref- 
erence to  Fig.  9. 

Conventional  Representation  of  Screw  Threads 


Right  Hand 


Fig.  9 


Right  Hand 


BOLTS  AND  NUTS 

(54)  Bolts.  There  are  three  distinct  classes  of  bolts 
in  use  at  the  present  time  called  carriage,  machine,  and 
stud  bolts.  Each  is  made  from  a  rod  of  iron,  threaded 
on  one  end  to  receive  a  nut,  and,  with  the  exception  of  the 
stud  bolt,  having  the  other  end  shaped  into  some  form  of 
head. 


Carriage-Bolt 


Fig.  10 


Carriage  bolts.  A  carriage  bolt  may  be  denned  as 
a  bolt  with  an  oval  head;  its  shank  is  squared  from 
%"  to  94"  under  the  head,  the  side  of  this  square  being  a 


96 


MECHANICAL  DRAFTING. 


little  larger  than  the  diameter  of  the  bolt.  This  bolt  is 
used  in  woodwork  and  when  drawn  into  a  hole  the  square 
under  the  head  takes  a  grip  in  the  wood  and  prevents 
turning  while  the  nut  is  drawn.  The  nut  being  thinner 
than  the  ordinary  nut  the  whole  effect  is  to  give  a  more 
finished  appearance  to  this  class  of  work,  especially  after 
painting.  Fig.  10  is  given  to  further  explain  this  class 
of  bolts. 


Fig.  11 


Machine  bolts.  Machine  bolts  are  divided  into  a 
number  of  classes,  each  class  being  named  either  from 
its  peculiar  shape  or  its  distinctive  use.  The  dimensions 


FASTENERS.  97 

of  the  several  parts  of  all  such  bolts  have  been  standard- 
ized, tables  arranged,  and  the  construction  and  size  of 
every  part  of  any  particular  size  bolt  is  perfectly  definite. 

Hexagonal  and  square-headed  bolts.  Inasmuch  as 
these  two  classes  of  bolts  are  usually  dealt  with  in  the 
same  table  of  dimensions,  it  will  perhaps  be  as  well  to 
include  both  in  this  discussion.  In  Fig.  11  is  shown 
the  conventional  manner  of  representing  hexagonal  and 
square-head  bolts  in  a  mechanical  drawing.  It  will  be 
noticed  that  the  hexagonal  bolt  is  so  placed  that  three 
faces  of  both  the  bolt  head  and  the  nut  are  visible  and 
the  square  head  bolt  is  so  placed  that  two  of  its  faces  are 
visible.  This  placing  should  be  strictly  adhered  to,  espe- 
cially in  machine  sketching  where  it  may  be  necessary  to 
show  the  kind  of  bolt  by  only  one  view. 

Likewise  it  will  be  seen  that  on  both  bolts  the  outer 
corners  of  the  heads  and  nuts  have  been  ground  or  turned 
off  until  the  face  of  the  head  and  nut  is  a  circle  tangent 
to  the  hexagonal  or  square  limits  of  the  head  or  nut. 
This  bevel  on  the  head  or  nut  is  called  the  chamfer  of 
the  head,  etc. 

In  constructing  the  end  view  of  any  bolt  the  chamfer 
circle  is  first  drawn  (the  diameter  of  this  chamfer  circle 
will  be  found  in  table  under  head  of  (t Distances  Across 
Flats"  or  "Short  Diameter")  and  the  hexagon  or  square 
circumscribed  by  means  of  the  30°x60°  or  45°  triangles. 
No  other  method  should  be  used  for  obtaining  the  hex- 
agon or  square. 

The  geometric  construction  of-  these  bolts  should  be 
entirely  familiar  to  the  draftsman,  and  Fig.  11  should  be 
thoroly  studied  and  mastered  in  every  detail.  Fig.  12 
should  also  be  consulted  in  this  connection. 


MECHANICAL  DRAFTING. 


Oval  Fillister  Hd.  Mach.  Screw 

'''TMp'l'm    't'.^[/j/f~^py^ 


Flat  Fillister  lid.  Mach.  Screw 


Round  Hd.  Mach.  Sc 


Flat     Conical        Oval       Dog 


Pig.  12 


FASTENERS. 


99 


Stud  bolt.  On  account  of  the  particular  use  and  form 
of  the  stud  bolt  it  deserves  special  mention.  It  has  no 
head  and  is  threaded  on  both  ends  nearly  up  to  its  center. 
In  places  where  a  headed  bolt  is  impracticable  the  stud 
bolt  is  screwed  into  the  tapped  hole  in  the  piece  of  metal; 
the  part  to  be  clamped  in 
place  is  then  slipped  on 
the  projecting  end  and  an 
ordinary  nut  used  to  draw 
the  piece  tight.  The  bolt 
thus  serves  the  second 
purpose  of  being  a  guide 
in  assembling  which  makes 
it  almost  indispensable  in 
places  where  machine 
parts  are  removed  and  re- 
placed very  often.  Fig. 
13  illustrates  this  impor- 
tant bolt. 


Fig.  13 


Nuts.  A  carriage  or  machine  bolt  nut  may  be  denned 
as  a  square  or  hexagon  of  steel  or  wrought  iron  of  any 
desired  thickness  with  a  threaded  hole  thru  the  center. 
They  need  no  classification,  since  they  differ  only  in 
shape,  thickness  and  finish.  They  may  be  square  or 
hexagonal,  very  thick  or  quite  thin,  and  if  rough  they 
quite  likely  have  been  punched  from  sheets  of  wrought 
iron  or  steel,  while  the  finished  nuts  have  been  cut  from 
square  or  hexagonal  bars  of  steel,  Fig.  11. 

DIMENSIONING  BOLTS 

(55)  Length,  diameter.  The  length  of  a  bolt  is 
always  understood  to  be  the  distance  from  the  end  to 


100  MECHANICAL  DRAFTING. 

the  under  surface  of  the  head.  In  placing  a  note  on  a 
drawing  designating  the  size  of  bolt  used,  the  diameter, 
length,  and  pitch  of  thread  should  be  given  in  the  order 
named,  followed  by  the  kind  of  bolt  wanted;  e.g., 
l"x  4"x  8  thrds.  per  in.  Fin.  Hex.  Bolt.  If  the  bolt  is  to 
be  a  U.  S.  Std.  bolt,  only  the  length  and  diameter  are 
needed.  On  large  or  long  bolts  the  threaded  length 
should  be  given. 

SCREWS 

(56)  Definition.  A  screw  may  be  defined  as  a  rod 
of  iron  or  steel  threaded  on  one  end  and  containing  a 
square,  hexagonal,  or  slotted  head  on  the  other  by  which 
the  screw  is  turned.  Screws  are  divided  into  four  gen- 


nj     \M\i\v\\\jg> 


Lag  Screw 


Wood  Screw 

ShouJder.    Scrcv 


Fig.  14 

eral  classes — wood,  set,  cap,  and  machine  screws.  Figs. 
12  and  14  illustrate  some  of  the  types  most  commonly 
used.  Tables  of  dimensions  may  be  found  in  the  Appen- 
dix. 

In  listing  screws  on  a  drawing  the  method  outlined 
in  Art.  55  for  bolts  should  be  followed. 


FASTENERS. 


PIPE  THREADS 


101 


(57)  Many  times  the  engineer  is  required  to  deal 
with  plans  in  which  water,  steam  or  gas  pipes  are  used. 
In  order  to  make 
all  connections  wa- 
ter or  steam-tight 
the  threads  are 
turned  with  a 
standard  taper  of 
V  to  16".  Care 
should  be  taken  to  specify  this  kind  of  thread  when 
used  on  a  drawing  and  to  designate  its  size  by  giving 
the  inside  diameter  of  the  pipe  and  not  the  outside  diam- 
eter as  is  done  on  bolts  and  screws.  Fig.  15  further  illus- 


Complete  Threads 


Imperfect  Threads 
Fig.   15 


Starter  or  Taper  Tap 


Medium  or  Plug- 


Finishing  or  Bottoming 

Fig.  16 

trates  this  type  of  thread.     Tables  of  pipe  sizes  and 
threads  will  be  found  in  the  Appendix. 


102 


MECHANICAL  DRAFTING. 

SHOP   OPERATIONS 


(58)  Taps  and  Dies.  The  usual  method  of  cutting  V 
threads  is  by  means  of  tools  known  as  taps  and  dies. 
Figs.  16  and  17  furnish  general  information  concerning 
these  shop  tools.  The  tap  is  used  for  cutting  the  threads 


Dies. 


Fig.   17 


in  nuts  and  also  for  threading  holes  drilled  in  parts  of 
machines.  Dies  are  used  for  threading  bolts  and  screws 
and  other  rods  of  iron  not  greater  than  V  in  diameter. 


FASTENERS. 


108 


Fig.  20 


"Woodruff  Key 


104  MECHANICAL  DRAFTING. 

Square  threads,  threads  not  having  a  standard  pitch, 
and  all  large  threads  are  turned  on  the  lathe. 

KEYS  AND  KEYWAYS 

(59)     In  fastening  wheels,  pulleys,  etc.,  to  shafts  two 
classes  of  fasteners  may  be  used,  set-screws  or  keys. 
Set-screws  may  be  used  to  advantage  in  all  cases  in  which 
the  twisting  force  on  the  shaft  is 
very  small.    It  is  not  wise  to  use 
such  a  fastener  on  large  pulleys 
or  in  cases  in  which  the  load  is 
likely  to  be  very  great.    In  this 
latter  case  one  of  three  varieties 
of  key  may  be  used  according  to 
the  nature  of  the  machine.    These 
keys  and  keyways  are  (a)  Keys 
on  flats,  Fig.   18;   (b)   Straight  Fig.  21 

seated  keys,  Fig.  19;  (c)  Wood- 
ruff keys,  Fig.  20;  (d)  Round  keys,  Fig.  21.  It  is  clearly 
seen  that  the  first  type  of  key  has  a  very  limited  use,  and 
owing  to  the  fact  that  the  Woodruff  key  is  patented,  the 
straight  keys  and  seats  have  the  most  general  use.  In 
this  type  of  key,  it  is  seen,  Fig.  19,  that  one-half  of  the 
recess  is  milled  or  cut  into  the  shaft  (this  groove  being 
known  as  a  keyseat)  while  the  other  half  of  the  recess  is 
cut  into  the  hub  of  the  pulley  and  is  known  as  the  keyway. 
When  fitted  over  each  other  they  should  form  nearly  a 
square,  the  height  being  slightly  less  than  the  width.  The 
keys  used  in  this  connection  are  cut  from  square  bars  of 
cold  rolled  steel  and  filed  to  a  slight  taper  on  one  side 
only,  so  that  when  driven  in  far  enough  they  wedge 


FASTENERS.  105 

between  the  hub  and  shaft,  thereby  preventing  the  pulley 
both  from  sliding  along  the  shaft  in  either  direction  and 
from  turning  about  the  shaft. 


106  MECHANICAL  DRAFTING. 

CHAPTER  6 

SHOP  TEEMS,  TOOLS,  MACHINES 
Draftsman's  Use  of  Shop  Terms. 

(60)  Certain  terms  that  are  in  common  use  in  the 
workshop  are  used  by  the  designer  and  draftsman  in  the 
form  of  a  direction  to  the  workman.     Such  words  as 
"drill,"  "tap,"  "ream,"  "finish,"  etc.,  are  shop  terms 
directing  the  workman  to  perform  the  operation  indi- 
cated.   When  these  words  are  used  on  a  drawing,  the 
lettering  should  be  so  placed  that  there  will  be  no  con- 
fusion in  determining  to  exactly  what  part  of  the  ob- 
ject the  term  applies.    Leaders  should  point  to  the  part 
referred  to  if  the  meaning  is  not  clear  without  them.    If 
additional  wording  other  than  the  simple  term  is  needed, 
the  English  language  should  be  used  in  such  a  way  that 
the  meaning  of  the  note  cannot  be  misunderstood. 

Ordinarily,  working  drawings  sent  to  the  shop  are 
made  so  complete  that  the  same  drawing  will  answer  for 
the  pattern-maker,  blacksmith,  and  machinist.  In  this 
case,  each  workman  uses  only  that  part  of  the  information 
on  the  drawing  that  applies  to  his  work.  Some  large 
shops  follow  the  method  of  making  a  separate  drawing 
for  each  of  these  workmen,  so  that  he  will  be  supplied 
only  with  the  dimensions  and  notes  that  apply  to  his  par- 
ticular work. 

FINISH 

(61)  A  casting  or  forging  is  in  a  rough  state  when  it 
comes  from  the  foundry  or  forge  shop  and  if  certain  parts 
are  to  be  machined,  they  are  marked  "finish"  or  simply 


SHOP  TERMS,  TOOLS,  MACHINES. 


J07 


"f"  on  the  drawing.  The  most  convenient  way  of  indi- 
cating that  a  surface  is  to  be  finished  is  to  place  the  letter 
"f"  across  the  straight  line  projection  of  the  surface. 
In  Fig.  1,  the  upper  and  lower  faces  of  the  block  are  to 


-4 


Drill 


-i 


I 
I 


toe.  i 


be  machined.  Since  the  dimensions  given  on  the  draw- 
ing indicate  the  size  of  the  finished  object,  surfaces 
marked  with  an  "f"  will  indicate  to  the  pattern-maker 
or  blacksmith  that  allowance  for  the  tool  cut  must  be 
made  on  the  casting  or  forging. 

The  note  "f  all  over"  placed  under  a  detail  drawing 
means  that  the  entire  surface  of  this  part  is  to  be  ma- 
chined. 

The  operations  coming  under  the  head  of  "finish"  will 
in  general  be  performed  on  lathes,  planers,  or  shapers 
such  as  are  shown  in  accompanying  cuts. 


108 


MECHANICAL  DRAFTING. 

MILL 


(62)  In  the  shop  operation  required  in  cutting  slots, 
grooves  known  as  key  seats,  also  other  similar  opera- 
tions, Fig.  2,  a  machine  known  as  a  milling  machine 


Cut  on  Milling  Machine 


Pig.  2 

is  used.  The  cutting  tools  resemble  the  common  type 
of  circular  saw  and  operate  on  the  same  principle.  As 
seen  on  pages  109  and  110,  which  are  horizontal  milling- 
machines,  the  cutter  is  fastened  rigidly  to  the  revolving 
shaft  or  arbor  while  the  piece  of  material  to  be  machined 
is  clamped  to  the  table  and  the  table  moved,  either  by 
hand  or  automatically,  slowly  under  the  cutter,  as  a  log 
is  fed  into  the  saw  of  a  sawmill.  For  special  work  mill- 
ing cutters  of  many  odd  designs  are  made,  as  seen  on 
pages  111  and  112.  The  machine  shown  on  page  113  is 
known  as  a  vertical  milling  machine,  the  shaft  or  arbor  in 
this  case  being  vertical.  To  prevent  vibration  in  the 
arbor  of  the  horizontal  machine  (this  vibration  being 


SHOP  TERMS,  TOOLS,  MACI11NKS. 


109 


HOBIZONTAL  MILLING  MACHINE 


110 


MECHANICAL  DRAFTING. 


HOKTZONTAL  MILLING  MACHINE 


SHOP  TERMS,  TOOLS,  MACHINES.  Ill 


MILLING  CUTTEES 


112 


MECHANICAL  DRAFTING. 


MILLING  CUTTERS 


SHOP  TERMS,  TOOLS,  MACHINES.  113 


VERTICAL  MILLING  MACHINE 


114 


MECHANICAL  DRAFTING. 


known  as  chatter)  and  consequent  rough  work  of  the  cut- 
ter, chatter  braces,  shown  below,  are  being  put  on  most 
machines  of  late  design.  The  note  used  to  indicate  any 
desired  milling  operation  may  be  as  follows:  "2"  mill"; 
the  two  inches  indicating  the  diameter  of  the  milling 
cutter;  or  "Mill  %"  key  seat,  4"  long,"  "Mill  i/8"  slot, 
W  deep,"  etc. 


HOEIZONTAL  MILLING  MACHINE  WITH  CHATTER  BRACES 

Since  economy  of  time  is  a  large  item  in  shop  work 
the  designer  will  do  well  to  study  carefully  the  many  pos- 
sibilities of  the  milling  machine.  Next  to  the  lathe  and 
drill  it  is  perhaps  the  most  efficient  machine  in  use. 


SHOP  TERMS,  TOOLS,  MACHINES.  115 


TWIST  DBILLS 


116  MECHANICAL  DRAFTING. 


DRILL  PRESS 


SHOP  TERMS,  TOOLS,  MACHINES.  117 

DRILL 

(63)  The  term  "drill"  may  be  applied  to  all  holes  of 
small  diameter  up  to  two  inches,  which  do  not  need  a  high 
finish.    Holes  which  are  to  be  tapped  for  screws  or  which 
are  to  receive  a  bolt  or  which  are  later  to  be  finished  to 
a  larger  diameter  with  a  reamer  may  be  cut  on  a  drill 
press  with  a  twist  drill.     On  pages  115  and  116  are 
shown  twist  drills  and  drill  presses  of  various  designs 
used  in  performing  the  shop  operation  termed  "drill." 

BORE 

(64)  In   all   cases   where   a   round   hole   is   to   be 
machined  and  the  hole  is  either  so  large  that  a  twist  drill 
cannot  be  used  or  it  is  desired  to  give  such  a  finish  to  the 
hole  as  is  impossible  in  the  inevitably  somewhat  rough 
work  of  the  twist  drill,  the  work  will  be  done  on  a  lathe 
by  means  of  the  short  boring  tools  or  by  cutting  tools  in 
connection  with  the  boring  bar  and  the  operation  will  be 
termed  boring  instead  of  drilling.    The  note  referring  to 
such  an  operation  is  1"  bore,  etc.,  the  dimension  referring 
to  the  diameter  of  the  hole.     Such  boring  operations 
are  performed  on  a  lathe  or  boring  machine,  pages  118 
and  119,  and  are  ordinarily  necessary  on  holes  whose 
diameters   are  greater  than  two  inches.     Twist  drills 
larger  than  two  inches  in  diameter  are  not  in  very  com- 
mon use  as  it  requires  an  extremely  heavy  drill  press  to 
operate  them  satisfactorily. 

If  a  cylindrical  part  is  to  fit  into  a  bored  hole,  the 
terms  "driving  fit,"  "forced  fit,"  "turning  fit,"  etc.,  will 
tell  the  kind  of  fit  that  is  required. 

The 'dimension  given  will  indicate  the  size  of  the  part 


MECHANICAL  DRAFTING. 


SHOP    TERMS,  TOOLS,  MACHINES 


119 


120 


MECHANICAL  DRAFTING. 


REAMERS 


REAMERS 


SHOP  TERMS,  TOOLS,  MACHINES.  121 

to  be  fitted  into  the  hole  and  the  necessary  allowance 
for  the  desired  fit  will  be  made  in  the  boring  operation. 

REAM 

(65)  Wherever  a  small  hole  is  to  be  given  a  certain 
taper  or  is  to  be  given  a  finish  not  possible  with  a  twist 
drill  or  is  to  be  cut  to  a  very  exact  dimension,  a  tool 
known  as  a  reamer,  page  120  should  be  used  and  the  term 
applying  to  such  an  operation  is  ream.    This  operation 
of  course  presupposes  that  a  hole  slightly  less  in  diam- 
eter has  already  been  cut  with  a  twist  drill,  or  bored  on 
a  lathe. 

CORE 

(66)  The  term  core  is  used  in  connection  with  cast- 
ings only  and  indicates  that  the  hole  referred  to  is  to 
be  produced  by  a  core  (a  hardened  cast  of  sand  of  the 
desired  shape  and  size),  which  is  placed  in  the  mold 
when  the  casting  is  made.    The  pattern-maker  must  make 
provision  for  the  core  in  the  construction  of  the  wood 
pattern  of  the  casting. . 

"Core  V/a""  means  that  a  core  1%"  in  diameter  will 
be  used  in  the  mold.  The  cored  hole  will  of  course  be 
as  rough  as  the  surface  of  a  rough  casting. 

TAP 

(67)  The  term  tap  applies  to  the  shop  operation 
required  in  cutting  V  threads  in  holes  of  comparatively 
small  diameter ;  that  is,  less  than  one  and  one-half  inches. 
The  note  used  to  indicate  that  a  certain  hole  is  to  be 
threaded  to  a  certain  pitch  is  as  follows :  %"  tap  x  13  pi. 


122 


MECHANICAL  DRAFTING. 


On  pages  101  and  102  are  shown  a  series  of  standard 
taps  and  likewise  both  bolt  and  pipe  dies  used  in  cutting 
V  threads  on  bolts,  pipes,  etc. 

TAP  DRILL 

(68)  A  tap  drill  is  a  twist  drill  of  the  common  type, 
named  a  tap  drill  in  this  case  because  it  has  been  used 
in  drilling  a  hole  which  is  to  be  threaded  to  receive  a 
screw. 

HARDEN,  TEMPER,  ANNEAL 

(69)  These  are  terms  which  have  to  do  with  the  heat 
treatment  of  the  machine  parts  in  question  and  there- 
fore will  be  interpreted  by  the  workmen  in  the  forge 
shop. 

FILLET 

(70)  It  is  a  well  recognized  principle  of  mechanics 
that  a  break  is  much  more  likely  to   occur  in  sharp 


Fig.  3 


Fig.  4 


corners  of  a  machine  than  elsewhere,  the  corner  seem- 
ing to  furnish  a  starting  point  for  the  break.  For  this 
reason,  and  others  which  need  not  be  mentioned,  all 
corners  found  on  castings  are  seen  to  be  slightly  rounded, 


SHOP  TERMS,  TOOLS,  MACHINES.  123 

Fig.  3.  This  rounded  corner  is  known  as  a  fillet;  like- 
wise the  material  which  is  used  to  make  this  fillet  in  pat- 
terns takes  the  same  name.  In  Fig.  4  is  shown  the 
method  of  making  such  filleted  corners  in  patterns.  The 
triangular  piece  shown  is  made  of  wood,  shaped  by  driv- 


Shape  of  the  Fillet 
Fig.  5  Fig.  6 

ing  thru  a  Die,  Fig.  5,  as  dowel  pins,  or  of  hard  wax 
rounded  by  a  heated  rod,  Fig.  6,  or  it  may  be  of  leather 
which  can  be  purchased  in  coils  of  any  length.  The 
leather  fillets,  of  course,  are  most  convenient  for  very 
irregularly  shaped  pieces.  The  radius  of  the  arc  of  such 
fillets  is  quite  generally  14";  however,  it  is  necessarily  a 
matter  of  machine  design  and  for  very  large  pieces  the 
radius  must  be  greater  than  14". 

BEARINGS 

(71)  Brasses.  In  certain  types  of  machines  it  is 
desirable  to  use  brass  for  bearings  rather  than  the  com- 
bination of  lead  and  zinc  and  copper.  Such  bearings  are 
ordinarily  made  in  halves,  constructed  so  as  to  permit 
of  a  slight  adjustment,  Fig.  7.  These  half  bearings  are 
commonly  known  as  brasses. 

Babbit.  The  alloy  of  lead,  zinc  and  copper  mentioned 
above  is  commonly  known  as  babbit.  The  greater  the 
amount  of  zinc  and  copper,  the  harder  this  compound  is. 
Two  of  the  material  advantages  of  babbit  for  bearings 


124 


MECHANICAL  DRAFTING. 


are,  that  the  metal  is  cheap,  and  such  bearings  can  be 
easily  replaced  by  a  workman  of  but  ordinary  experience. 
Babbit  lining  is  poured  while  molten  into  the  cast  iron 
casings  with  the  shaft  in  place. 


Fig.  7 


LIBRARV 

SCHOOL 


ISOMETRIC   AND   OBLI 

MANUAL  ARTS  *ND  HOME  ECONOI 
SANTA  BARBARA,  CALIFORNIA 

CHAPTER  -7 


ISOMETRIC  AND  OBLIQUE  PROJECTION 
EXPLANATION  OF  PRINCIPLES 

(72)  If  through  a  given  point  called  the  origin  three 
lines  be  drawn  at  right  angles  to  each  other,  as  the  three 
adjacent  edges  of  a  cube,  we  have  the  usual  mathemat- 
ical coordinate  axes  X,  Y,  and  Z.  These  axes  taken  in 
pairs  determine  three  planes,  such  as  the  three  coordi- 
nate planes  used  in  Chapter  3.  If  now  an  object  with 
rectangular  or  square  faces,  for  example  a  cube,  be  placed 
in  the  first  angle,  and  be  viewed  in  turn  in  the  direction 
of  the  axes  X,  Y,  and  Z,  the  figure  in  each  case  will  appear 
to  be  simply  a  square.  These  squares  projected  on  their 
respective  coordinate  planes  give,  of  course,  the  ortho- 
graphic projections  of  the  cube,  and  it  should  be  remem- 
bered that  the  square  seen,  if  the  cube  is  viewed  in  the 
direction  of  the  X  axis,  represents  the  entire  object  and 
not  merely  the  face  of  it.  Thus  we  see  that  one  face 
only  is  visible,  in  general,  in  each  view. 

If  now  we  imagine  a  line  drawn  in  such  a  direction 
as  to  make  equal  angles  with  X,  Y,  and  Z,  for  example, 
the  diagonal  of  the  cube,  and  view  the  object  in  the  direc- 
tion of  this  line,  it  is  apparent  that  three  faces  will  be 
visible,  although  now  none  shows  as  a  rectangle,  nor  do 
we  see  any  of  the  edges  in  their  true  lengths.  However, 
all  the  edges  of  the  cube  parallel  to  axes  X,  Y,  and  Z 
are  equally  or  proportionally  fore- shortened  if  seen  in 
the  direction  of  this  new  axis,  known  as  the  isometric 
axis.  The  plane  perpendicular  to  the  isometric  axis  is 


126 


MECHANICAL  DRAFTING. 


known  as  the  isometric  plane,  and  the  projection  on  this 
plane  of  any*  object  viewed  in  the  direction  of  the  iso- 
metric axis  is  known  as  an  isometric  projection.  The 
sheet  of  paper  or  blackboard  may,  of  course,  be  conceived 
as  the  isometric  plane,  on  which  the  projections  of  the 
three  axes  X,  Y,  and  Z  will  be  right  lines  making  120 
degrees  with  each  other  and  the  projection  of  the  iso- 
metric axis  will  be  their  point  of  intersection,  Fig.  1. 
This  point  of  intersection  may  also  be  termed  the  origin. 


Fig.  2 


Fig.  3 


DIRECTRICES 

(73)  The  orthographic  projections  on  the  isometric 
plane  of  the  three  coordinate  axes  X,  Y,  and  Z  are  known 
in  the  drawing  as  the  directrices,  and  occasionally  as  the 
isometric  axes.  Since  the  coordinate  axes  make  with  each 
other  equal  angles,  their  projections  (the  directrices) 
also  make  equal  angles  (120  degrees)  with  each  other. 
This  being  true,  when  it  is  desired  to  make  any  isometric 
projection,  the  directrices  may  be  drawn  immediately 
through  any  chosen  point  and  at  120  degrees  to  each 
other.  One  of  the  directrices  is  usually  taken  vertical, 
Fig.  1 ;  however,  the  arrangements  shown  in  Figs.  2  and 
3  are  frequently  used. 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 

ISOMETRIC  SCALE 


127 


(74)  Since  the  coordinate  axes  are  oblique  to  the 
isometric  plane,  their  projections  are  shorter  than  the 
axes  themselves.  However,  since  each  axis  makes  the 
same  angle  with  the  isometric  plane,  one  inch  measured 
on  each  of  the  three  axes  will  project  in  equal  lengths 
on  tho  isometric  plane.  For  all  ordinary  purposes,  in 


Origin 


Fig.  4 

making  an  isometric  projection,  it  is  more  convenient  to 
lay  off  the  projections  of  lines  which  are  parallel  to 
X,  Y,  and  Z  equal  in  length  to  the  actual  lines.  It  is 
seen,  of  course,  that  the  projection  made  with  such 
measurements  represents  the  object  as  being  about  fifty 
per  cent  larger  than  it  actually  is.  Since  the  direct  use 
of  the  scale  in  measuring  these  lines  full  length  makes 
so  much  for  convenience  and  only  enlarges  the  view,  this 
procedure  is  usually  followed.  If,  on  the  other  hand, 
it  is  desired  that  the  projection  be  mathematically  cor- 
rect, the  projection  of  all  lines  parallel  to  X,  Y,  and  Z 
must  be  measured  according  to  the  isometric  scale.  Since 
each  coordinate  axis  makes  with  the  isometric  plane  an 


128 


MECHANICAL  DRAFTING. 


angle  of  35°  16',  if  we  assume  the  hypotenuse  AB  of  the 
right  triangle,  Fig.  4,  to  be  one  of  the  coordinate  axes, 
BC  the  isometric  axis,  and  CA  the  isometric  plane,  viewed 
edgewise,  the  isometric  projection  of  any  given  length 
BE  on  the  axis  BA  would  project  on  the  plane  with  a 


Fig.   5 

length  equal  to   Ce.     Figs.   5   and  6  illustrate  simple 
methods  for  obtaining  the  isometric  scale. 

(75)     Problem  1.    To  construct  the  isometric  projec- 
tion of  any  parallelepiped. 

Construction.    Cube  2"  on  edge,  Fig.  7. 

Thru  point  0  are  drawn  the  axes  OB,  OA,  and  OC, 
making  with  each  other  angles  of  120 
degrees.  From  0,  along  OA,  measure 
with  the  isometric  scale  2";  the  same 
along  OC  and  OB  to  points  D,  E,  and 
F.  OD  and  OE  then  represent  the 
two  adjacent  sides  of  the  base,  and 
lines  from  D  and  E  parallel  to  OE  and 
OD  complete  the  base.  In  similar 
manner  the  vertical  faces  DOF  and  Fig-  7 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 


129 


FOE  are  completed;  then  draw  the  top  base  FS  and 
finally  the  faces  SD  and  SE. 


IRREGULAR  OBJECTS 

(76)  Inasmuch  as  all  but  a  very  small  percentage  of 
machine  parts  are  either  of  rectangular  shape  or  can 
easily  be  enclosed  in  such 

a  box  or  parallelepiped, 
the  isometric  projections 
of  irregular  objects  are 
easily  constructed  with  the 
aid  of  such  an  enclosing 
parallelepiped,  Fig.  8.  In 
most  cases  it  will  be  found 
necessary  to  section  the 
object  in  order  to  show 
the  interior  portion  or 
cross-section,  Figs.  9  and 

Pig.  8 

CIRCLES 

(77)  Problem  2.    To  construct  the  isometric  projec- 
tion of  a  circle,  Fig.  11. 

8  point  method.  ABCD  is  the  isometric  projection  of 
a  square  in  which  a  circle  is  inscribed.  On  edge  AB  con- 
struct a  square  and  inscribe  in  it  a  circle.  Draw  the  hori- 
zontal diameter  of  this  circle  and  diagonals  of  the  square. 
The  points  of  tangency  of  the  circle  with  the  square  and 
the  4  points  of  intersection  with  the  diagonals  constitute 
the  desired  8  points.  If  the  diagonals  of  the  parallel- 
ogram be  drawn  the  isometric  projections  of  these  8 


130 


MECHANICAL  DRAFTING. 


Pi«.  10 


ISOMETRIC    AND   OBLIQUE   PROJECTION. 


131 


points  may  be  obtained  as  shown  and  the  ellipse  drawn 
thru  them  by  means  of  the  irregular  curve. 


Fig.   11 


Approximate  mechanical  method.  The  isometric 
projection  of  a  circle  which  lies  in  a  plane  parallel  to 
the  plane  of  any  two  isometric  axes  will  always  be  an 
ellipse  inscribed  in  a  rhombus  ABCD,  whose  acute  angles 
A  and  0  are  60  degrees,  and  which  itself  is  the  isometric 
projection  of  the  square  circumscribing  the  circle  repre- 
sented. The  ellipse  may  be  approximated  with  satisfac- 
tory exactness  if  made  of  arcs  of  circles  as  illustrated  in 
Fig.  12.  From  the  obtuse  angles 
B  and  D  perpendiculars  are 
dropped  to  the  opposite  sides. 
Then  with  radius  R  equal  to  DE 
and  centers  B  and  D  vthe  arcs  HF 
and  GE  are  described;  with  cen- 
ters K  and  L,  and  radius  r  equal 
to  LE,  the  small  circles  are  de- 
scribed completing  the  approxi- 
mate ellipse.  Fie-  12 


132 


MECHANICAL  DRAFTING. 

DIMENSIONING 


(78)  In  placing  dimensions  on  an  isometric  drawing, 
the  same  rule  must  be  followed  as  in  orthographic  work- 
ing drawings ;  the  dimensions  must  read  from  left  to  right 
or  from  the  bottom  up.  In  following  this  rule  it  will  be 
found  always  that  the  dimension  lines  are  parallel  to  the 
coordinate  axes,  never  otherwise.  In  giving  the  diam- 


Fig.   13 

eters  of  circles  the  method  shown 
in  Fig.  13  is  preferable  to  plac- 
ing the  diameter  directly  on  the 
isometric  of  the  circle.  On  in- 
spection of  Fig.  14  it  is  seen  that 
there  are  actually  three  faces  of 
the  object  to  be  dimensioned  and 
in  giving  the  dimensions  for  face 
No.  1,  which  is  parallel  to  the 
isometric  plane  No.  1,  it  must  first 
be  decided  what  directions  consti- 
tute from  left  to  right  and  from  bottom  up.  The  same 
thing  must  be  decided  for  faces  2  and  3.  In  Fig.  15  is 
given  a  key  which  will  be  useful  in  dimensioning.  In  con- 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 


133 


nection  with  this  key  it  will  be  necessary  for  the  student, 
in  placing  dimensions,  to  decide  merely  to  which  face  of 
this  key  his  dimensions  are  parallel,  Figs.  9  and  10. 

OBLIQUE  PROJECTION 

(79)  Inasmuch  as  circles  are  so  rarely  found  in  such 
positions  that  their  projections  are  true  circles  in  iso- 
metric projection,  a  variety  of  projection  has  been  de- 
vised in  which  it  is  possible  so  to  place  circles  that  their 
projections  are  circles  and  are  easily  drawn.     This  is 
known  as  oblique  projection. 

In  oblique  projection  as  in  the  isometric  projection 
just  discussed,  we  have  one  plane  of  projection.  The  line 
of  sight  is  always  assumed  oblique  to  the  plane  of  projec- 
tion. We  may  call  this  line  the  oblique  axis.  If  two  of  the 
coordinate  axes  are  placed  parallel  to  the  plane  of  projec- 
tion and  projected  thereon  by  lines  parallel  to  the  line  of 
sight,  the  projections  will  be  unchanged  in  relation  to 
each  other.  In  projection  the  third  axis  will,  however, 
be  foreshortened  and  inclined  to  the  other  two  at  an  angle 
other  than  90°.  This  angle  may  be  varied  at  will  accord- 
ing to  the  angle  of  inclination  of  the  oblique  axis  with  the 
plane  of  projection,  but  is 
usually  assumed  at  30°,  45°, 
or  60°  with  the  horizontal. 
These  projections  of  the 
coordinate  axes  are  called 
the  directrices. 

DIRECTRICES  AND  CO-ORDINATE  PLANES 

(80)  Thru  the  origin,  0,  Fig.  16,  (a)  and  (b),  are 
drawn  three  directrices  as  shown;  one  horizontal,  a  second 
vertical,  and  the  third  to  the  right  or  left  at  45°,  30°,  or 


134 


MECHANICAL  DRAFTING. 


60°  with  the  horizontal,  preferably  45°.  These  three  lines 
represent  lines  at  right  angles  to  each  other,  and  may  be 
compared  to  the  three  adjacent  edges  of  a  cube. 

Taken  two  and  two,  these  directrices  include  coordi- 
nate planes  as  follows :  OA  and  OB,  plane  1,  or  the  plane 
of  true  circles;  OB  and  OC,  plane  2,  a  second  vertical 
plane,  and  OA  and  OC,  plane  3,  a  horizontal  plane. 

DIMENSIONING 

(81)  In  oblique  as  well  as  in  isometric  projection, 
the  problems  of  dimensioning  are  threefold ;  i.  e.,  any 
object  drawn  may  have  faces  parallel  to  each  of  the  three 

coordinate  planes  in  Fig. 
17.  In  placing  dimensions 
for  constructions  on  these 
faces  it  is  necessary,  of 
course,  to  decide  what  di- 


Fig.   18 

rections  constitute  from  left  to  right  and  from  bottom  up. 
The  key  in  Fig.  18  may  be  used  in  a  manner  similar  to 
that  of  the  key  given  for  isometric  projection.  Inspec- 
tion of  Figs.  19-23  may  serve  to  clear  up  any  doubtful 
points,  both  in  dimensioning  and  in  construction. 

OBLIQUE  SCALE 

(82)     If  equal  distances  be  measured  from  0  along 
the  axes  OA,  OB  and  OC,  Fig.  24,  the  distance  along 


ISOMETRIC   AND   OBLIQUE   PROJECTION.  135 


Oblique  Projection  of  Stuffing  Box. 


Fig.   19 


136 


MECHANICAL  DRAFTING. 


Oblique  Projection  of  Shaft  Coupler. 
Fig.  20 


ISOMETRIC    AND   OBLIQUE   PROJECTION. 


137 


Fig.  21 


MECHANICAL  DRAFTING. 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 


139 


Oblique  Projection  of  Flanged  Pipe  Tee. 


Fig    23 


140 


MECHANICAL  DRAFTING. 


OC  will  appear  to  be  longer  than  those  along  OA  and 
OB ;  hence,  for  symmetry,  it  is  necessary  to  make  use  of 


Fig.  24 


Oblique  Scale  for  45'         Oblique  Scale  for  30' 
Fig.  25 


the  oblique  scale  in  measuring  any  distance  along  OC. 
The  oblique  scale  is  obtained  by  measuring  off  inches, 
etc.,  on  the  hypotenuse  of  a  45°,  30°,  or  60°  triangle  and 
projecting  these  inches  upon  either  of  the  legs  for  45°, 
long  leg  for  30°  and  short  leg  for  60°,  Fig.  25. 

(83)  Problem  3.    To  draw  the  oblique  projection  of  a 
parallelepiped. 

Construction.    Cube  V  on  edge. 

Thru  a  chosen  point,  0,  Fig.  26,  draw  the  three  axes 
OA,  OB,  and  OC.  Along  axes  OA 
and  OB  measure  V  to  D  and  S, 
and  with  the  oblique  scale  meas- 
ure 1"  along  OC  to  B.  Com- 
plete the  parallelograms  ODMB, 
OSLB,  and  DNSO;  then  the  re- 
maining faces  may  easily  be 
added. 

CIRCLES 

(84)  Point  E,  in  face  TLBM,  Fig.  27,  is  the  center 
of  a  circle  34"  diameter.     Since  this  is  the  face  of  true 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 


141 


circles,  the  circle  may  be  constructed  with  the  compass. 
If  it  is  desired  to  draw  the  projections  of  circles  lying 
in  faces  TNSL  or  NTMD  the  8-point  method  explained 
in  isometric  projection  may  be  used.  In  cases  where 


rapidity  of  construction  is  more  important  than  sym- 
metry, it  is  common  practice  among  draftsmen  to  omit  the 
use  of  the  oblique  scale  altogether.  Then  if  the  oblique 
axis  be  drawn  at  an  angle  of  30  degrees  to  the  horizontal, 
it  will  be  noted,  in  Fig.  28,  that  face  NM  is  now  of  such 
shape  as  to  convert  the  oblique  projection  of  any  circle 
placed  in  that  face  into  an  isometric  projection,  and  the 
mechanical  method  of  constructing  that  isometric  pro- 
jection, shown  in  Fig.  12,  can  and  should  be  used.  If, 
on  the  other  hand,  the  oblique  axis  be  drawn  at  an  angle 
of  60  degrees  to  the  horizontal,  Fig.  29,  the  face  NL  is 
now  of  such  shape  as  to  convert  the  oblique  projection 
of  any  circle  placed  in  it  into  an  isometric  projection 
which  can  be  constructed  mechanically  by  the  method  of 
Fig.  12. 


142 


MECHANICAL  DRAFTING. 


With  some  care  it  will  usually  be  possible,  in  making 
the  oblique  projection  of  any  object  containing  circles, 
so  to  place  the  object  that  the  oblique  projections  of 
some  of  the  circles  are  true  circles,  while  the  projec- 
tions of  the  remainder  become  isometric  when  the  ob- 
lique axis  is  drawn  either  at  30  or  60  degrees  to  the 
horizontal. 


Fig.   29 


IRREGULAR  OBJECTS 


(85)  All  that  has  been  said  on  this  subject  under 
isometric  projection  applies  as  well  in  oblique  projection. 
It  is  perhaps  unnecessary  to  suggest  that  when  making 
any  oblique  projection  care  should  be  taken  so  to  place 
the  object  that  most  of  the  circles  will  appear  as  true 
circles. 


SHADES  AND  SHADOWS  IN  ISOMETRIC  AND   OBLIQUE 
PROJECTION 

(86)     Shades  and  shadows,  in  isometric  projection 
as  in  orthographic  projection,  are  used  merely  for  the 


ISOMETRIC   AND   OBLIQUE   PROJECTION.  143 

natural  appearance  which  they  give  to  a  drawing.  Hence, 
as  in  orthographic  projection,  the  draftsman  has  con- 
siderable freedom  in  determining  both  the  direction  and 
the  length  of  the  shadows.  Before  proceeding  with  a 
problem  in  shades  and  shadows  it  will  perhaps  be  well 
to  define  a  few  of  the  terms  and  state  the  fundamental 
principles  which  govern  construction. 

Direct  light.  All  light  which  comes  to  any  body  di- 
rectly from  the  source  (the  sun,  arc  lights,  etc.)  is  known 
as  direct  light. 

Indirect  light.  All  light  which  reaches  objects  in  an 
indirect  way,  e.  g.,  by  reflection  from  other  objects  which 
are  in  direct  light,  is  known  as  indirect  light. 

Shade.  Any  portion  of  the  surface  of  an  object  from 
which  the  direct  light  is  excluded  by  some  part  of  the 
same  object  is  said  to  be  in  shade.  This  shaded  surface 
may  also  be  known  as  a  shade. 

Shadow.  Any  portion  of  the  surface  of  an  object  from 
which  the  direct  light  is  excluded  by  some  part  of  another 
object  is  said  to  be  in  shadow,  and  for  convenience  may 
be  called  a  shadow. 

PRINCIPLES 

1.  All  rays  of  light  in  these  problems  are  regarded  as 
parallel;  hence,  when  the  direction  of  the  first  ray  has 
been  assumed,  all  others  must  be  considered  parallel  to  it. 

2.  The  shade  or  shadow  of  a  given  point  on  a  given 
surface  is  the  point  in  which  a  ray  thru  the  given  point 
pierces  the  given  surface. 

3.  Any  ray  used  to  determine  the  shade  or  shadoiv  of 
a  given  point  may  in  reality  be  a  ray  of  light ;  however, 


144 


MECHANICAL  DRAFTING. 


in  this  discussion  it  will  be  known  as  a  shadow  ray;  see 
Miller's  Descriptive  Geometry,  Art.  124. 

4.    If  a  line  AB  is  parallel  to  a  plane,  e.  g.,  H,  the 
shadow  of  AB  on  H  is  parallel  and  equal  in  length  to  AB. 


Fig.  30 


5.  If  lines  AB  and  CD  are  parallel  the  shadows  of 
AB  and  CD  on  any  plane  must  be  parallel,  i.  e.,  the 
shadows  of  parallel  lines  are  parallel. 

6.  If  a  line  AB  is  oblique  to  H,  AB  and  its  shadow 
on  H  will  meet  at  the  point  in  which  AB  pierces  H. 

7.  The  shadows  of  parallel  lines  on  parallel  planes 
are  parallel. 

(87)     Problem  4.     To  find  the  isometric  or  oblique 
projection  of  the  shade  and  shadow  on  H  of  a  given  object. 

Given.     Isometric  and  oblique  projections  of  Cross, 
Figs.  30  and  31. 


ISOMETRIC   AND   OBLIQUE   PROJECTION. 


145 


Req'd.  Isometric  and  oblique  projections  of  shade  and 
shadow  on  H. 

Beginning  with  point  0  as  an  origin,  a  line  may  be 
drawn  in  any  desired  direction,  e.  g.,  Oa,  to  represent  the 
shadow  of  OA,  and  point  a  assumed  in  any  desired  posi- 


Fig.  31 


tion  as  the  shadow  of  point  A.  Aa  is  the  isometric  pro- 
jection of  the  shadow  ray  thru  A,  and  all  other  shadow 
rays  must  be  parallel  to  Aa.  Since  AB  is  parallel  to  H, 
its  shadow  db  is  parallel  and  equal  in  length  to  AB.  BC 
is  parallel  to  OA,  hence  its  shadow  be  is  parallel  to  Oa, 
and  c  is  determined  by  shadow  ray  Cc.  CD  is  parallel  to 
H,  hence  its  shadow  cd  is  parallel  and  equal  in  length  to 
CD;  d  may  likewise  be  located  by  the  shadow  ray  Dd. 
Since  the  plane  GCDK  is  parallel  to  H,  the  shade  of  GE 
on  this  plane  is  parallel  to  Oa,  see  Principle  7,  and  e  is 
located  by  the  shadow  ray  from  E.  EF  is  parallel  to 


146  MECHANICAL  DRAFTING. 

GCDK,  hence  the  shade  line  from  e  is  parallel  to  EF; 
to  find  the  shadow  of  F  draw  the  shadow  of  MF  parallel 
to  Oa;  the  intersection  of  this  shadow  line  with  the  ray 
thru  F  locates  f.  The  shadow  of  EF  is  paralled  to  cd; 
fn  is  parallel  and  equal  in  length  to  FN.  It  is  readily 
seen  from  the  direction  of  Oa  that  the  face  AOM  must  be 
in  shade,  likewise  BCD  and  GEFK  and  space  KGteh. 

The  isometric  projections  of  the  shadows  of  the  re- 
maining points  are  located  successively  as  those  already 
found. 


MACHINE  SKETCHING.  147 

CHAPTER  8 

MACHINE  SKETCHING 

(88)  Definition.    A  machine  sketch  may  be  roughly 
defined  as  a  freehand  working  drawing. 

To  the  engineer  no  one  accomplishment  is  of  more 
value  than  the  ability  to  make  rapidly  accurate,  legible 
machine  sketches. 

A  draftsman  or  shop  foreman  may  be  called  upon  at 
any  time  to  make  a  hasty  sketch  of  some  broken  machine 
part  which  perhaps  cannot  be  removed  without  shutting 
down  the  machine  for  a  day  or  two. 

A  construction  engineer  putting  in  some  new  machin- 
ery may  find  that  some  plates,  fixtures,  etc.,  designed 
especially  for  the  job,  are  all  wrong,  and  he  must  imme- 
diately send  in  sketches  of  what  is  wanted. 

A  bridge  engineer  may  find  his  work  held  up  by  the 
breaking  or  absence  of  some  peculiarly  shaped  piece,  or 
may  need  some  special  fixtures  to  handle  difficulties  pecu- 
liar to  the  job. 

Likewise,  it  is  understood  that  all  machine  forms  are 
devised  in  the  mechanic's  brain  and  must  be  placed  on 
paper  in  some  approximate  form  before  it  is  possible  to 
make  a  mechanical  working  drawing. 

In  all  of  these  and  hundreds  of  other  cases  which  are 
inevitable,  the  ability  to  sketch  rapidly  and  well  is  indis- 
pensable, and  the  man  who  finds  himself  called  upon  to 
make  a  sketch  and  is  not  well  grounded  in  its  principles, 
will  find  himself  seriously  handicapped. 

PAPER 

(89)  It  will  be  seen  that  the  nature  of  the  situations 


148  MECHANICAL  DRAFTING. 

which  require  sketching  will  demand  the  use  of  scratch 
paper  or  a  notebook.  Cross-section  paper  is  invaluable 
for  this  purpose,  as  it  aids  materially  in  the  rapid  and 
accurate  sketching  of  the  several  views. 

NATURE   OF  DRAWING 

(90)  As  in  a  mechanical  ivorking  drawing,  a  machine 
sketch  consists  of  a  number  of  views  (top  and  front;  top, 
front,  and  left  end,  etc.)  of  a  machine  or  machine  part. 
These  views  are  true  orthographic  projections,  hence 
projections  of  each  other,  as  in  working  drawings.  Never 
show  more  views  than  are  necessary  to  explain  clearly 
the  construction;  of  course,  two  are  a  minimum;  varia- 
tions in  this  respect  will  be  mentioned  later. 

PENCIL— SKETCH  STROKE 

(91)  For  sketching  it  will  be  better  to  use  a  com- 
paratively soft  pencil,  H  or  2H,  as  it  is  desirable  to  show 
marked  distinction  between  the  outlines  of  the  object  and 
dimension  and  section  lines. 

In  drawing  lines,  whether  short  or  long,  the  sketch 
stroke  should  be  used.  The  sketch  stroke  is  merely  a 
succession  of  short  strokes  in  the  desired  direction,  and, 
as  a  result,  the  line  will,  of  course,  be  somewhat  ragged, 
consisting  of  a  number  of  short  overlapping  lines.  How- 
ever, by  this  method  it  will  be  found  possible  to  approxi- 
mate a  straight  line  much  more  closely  than  by  a  con- 
tinuous stroke. 

SIZE  OF  DRAWING 

(92)  The  work  being  freehand   and  done  usually 
under   adverse   conditions,    sketches   are   not   made   to 
scale;    numerical   dimensions    are    depended   upon    en- 


MACHINE  SKETCHING.  149 

tirely  for  sizes.  As  an  aid  in  approximating  propor- 
tions of  the  different  parts  of  a  machine,  the  follow- 
ing scheme  will  be  found  useful:  Suppose  after  care- 
ful inspection  it  is  decided  that  only  two  views  are 
necessary,  and  these  front  and  right  end.  You  have 
perhaps  a  5  x  7  notebook  at  hand  and  must  place  these 
two  views,  with  dimensions,  on  this  size  sheet.  Estimate 
the  ratio  of  the  length  of  the  object  to  its  width  and 
height  and  block  out  roughly  on  the  sheet  the  proper  pro- 
portional spaces,  for  the  two  views,  making  them  as  largo 
as  possible.  Then  measure  off  on  a  lead  pencil  with  the 
thumb-nail  a  distance  equal  to  the  length  you  have  given 
the  space  for  the  front  view,  and,  holding  the  pencil  hori- 
zontally and  about  1'  from  the  eye,  move  off  from  the 
machine  until  the  space  from  the  end  of  the  pencil  to  the 
thumb-nail  just  covers  the  length  of  the  machine.  Stand- 
ing in  this  position  and  using  the  pencil  in  this  manner, 
the  several  parts  of  the  machine  may  be  rapidly  sketched 
in  their  proper  sizes. 

PROCEDURE 

(93)  In  making  a  machine  sketch,  the  greatest  speed 
and  accuracy  will  be  attained  by  following  some  system. 
The  following  will  be  found  valuable : 

1.  Decide  on  the  number  of  views  necessary,  and 
decide  which  these  should  be. 

2.  Estimate  ratio  of  length  to  width  of  machine  and 
block  out  on  sheet  proportional  spaces  for  above  views. 

3.  Sketch  in  all  outlines  (working  on  all  views  at 
the  same  time).    Do  not  attempt  to  finish  one  view  en- 
tirely before  working  on  the  other ;  when  a  line  is  placed 
on  one  view,  place  its  projection  on  the  other  view  so 
that  all  views  are  finished  at  approximately  the  same 
time. 


150  MECHANICAL  DRAFTING. 

4.  Sketch  in  dimensions,  auxiliary,  and  section  lines. 
The  reason  for  placing  on  dimension  lines  while  making 
up  the  views  is,  that  each  detail  of  the  piece  as  it  is 
drawn  may  suggest  a  necessary  dimension  that  perhaps 
would  be  overlooked  if  left  until  later.    A  break  should 
be  left  in  each  dimension  line.    No  attempt  need  be  made 
here  to  distinguish  between  outlines  and  other  lines. 

5.  Go   over  the   sketch  carefully  and  increase  the 
weight  of  outlines  so  that  the  construction  shows  easily. 

6.  Obtain  from  the  machine  with  calipers  and  rule 
all   dimensions    already   indicated    on    sketch.    Always 
place  on  overall  dimensions  as  a  check. 

7.  Be  liberal  with  notes. 

SHORT  CUTS 

(94)     To   save   time,   the   following   short   cuts   are 
permissible : 

1.  In  drawing  objects  of  familiar  shape,  wheels,  etc., 
the  hub,  two  spokes,  and  a  short  portion  of  the  rim  is 
sufficient. 

2.  Where  objects  are  symmetrical  with  respect  to  a 
center  line,  e.  g.,  gate  valves,  etc.,  it  is  sufficient  to  show 
only  one-half  of  object,  limiting  the  portion  drawn  by 
the  center  line.    The  other  half  may  be  drawn  in  when 
time  permits,  if  desired. 

3.  Where  objects  are  symmetrical  about  two  center 
lines  at  right  angles  to  each  other,  it  will  be  sufficient  to 
show  only  one-fourth  of  the  object. 

4.  Where  any  part  cannot  be  shown  well  in  detail, 
e.  g.,  bolts,  holes,  fasteners,  etc.,  explanatory  notes  may  be 
substituted— e.  g.,  %"  drill;  %"  x  10  pi.  tap;  %»  He*. 
Hd.  Mach.  Sc.;  etc. 


PERSPECTIVE.  151 

CHAPTER  9 

PERSPECTIVE 

(95)  Tho  it  is  impossible  to  give  here  any  complete 
explanation  of  the  principles  of  perspective,  it  has  been 
deemed  advisable  to  attempt  sufficient  explanation  to 
enable  one  to  understand  a  few  of  the  basic  principles. 

It  is  readily  seen  that  no  one  view  of  a  working  draw- 
ing of  any  object  can  present  to  the  eye  the  natural 
appearance  possessed  by  a  crayon  or  charcoal  drawing. 
The  reason  is,  that  in  making  a  working  drawing  the 
eye  was  imagined  at  an  infinite  distance  from  the  object, 
an  assumption  so  unnatural  as  to  give  rise  immediately  to 
results  of  an  unnatural  appearance. 

PERSPECTIVE  DRAWING 

(96)  Definition.   A  perspective  drawing  of  an  object 
is  such  a  representation  of  that  object  on  a  given  plane 
or  sheet  of  paper  as  will  present  the  same  appearance  as 
the  object  itself  when  the  eye  is  in  a  certain  position  with 
respect  to  the  object. 

The  plane  on  which  the  perspective  drawing  is  made 
is  called  the  picture  plane,  and,  for  reasons  which  need 
not  be  given  here,  is  usually  taken  vertically. 

PRINCIPLES  OF  CONSTRUCTION 

(97)  The  principle  on  which  perspective  construc- 
tion is  based  is  as  follows:    The  vertical  picture  plane 
is  placed  between  the  eye  and  the  object  (that  the  draw- 
ing may  be  smaller  than  the  object),  and  lines  of  sight 
or  visual  rays  drawn  from  the  eye  to  the  various  points 


152 


MECHANICAL  DRAFTING. 


of  the  object.  The  points  in  which  these  lines  pierce  the 
picture  plane  are  respectively  the  perspectives  of  the 
corresponding  points  of  the  object.  If  lines  be  drawn 
connecting  these  piercing  points  in  their  proper  order,  a 
perspective  drawing  of  the  whole  object  is  obtained. 
Fig.  1. 

PICTURE  PLANE  AND  POSITION  OF  OBJECT 

(98)     Since  perspective  drawings  are  made  mostly 
from  working   drawings,   the   vertical   plane   of    OrtJlO- 


graphic  projection  is  used  as  the  picture  plane  and  the 
object  placed  in  the  third  angle. 

POSITION  OF  POINT  OF  SIGHT 

(99)  The  point  of  sight  is,  of  course,  in  front  of  the 
vertical  plane,  and  may  be  in  either  the  first  or  fourth 
angles,  according  to  the  nature  of  the  view  desired;  i.  e., 
if  it  is  desired  to  make  a  drawing  showing  the  appear- 
ance of  the  object  when  directly  in  front  of  it,  the  point 
of  sight  would  be  in  the  fourth  angle. 

PRINCIPAL  POINT  IN  PERSPECTIVE 

(100)  The  projection  of  the  point  of  sight  on  the 
vertical  plane  is  called  the  principal  point  in  perspective, 
and  is  of  prime  importance  in  construction.    Inasmuch 


PERSPECTIVE. 


153 


as  the  vertical  projections  of  points  are  designated  thus, 
a',  b',  (f,  etc.,  the  vertical  projection  of  the  point  of  sight, 
S,  will  be  indicated  by  s'. 

PRINCIPAL  POINT  THE  VANISHING  POINT  OF  LINES 
PERPENDICULAR  TO  THE  PICTURE  PLANE 

(101)  It  is  a  familiar  fact  that  as  one  stands 
near  a  long  straight  section  of  railroad  track  the  two 
lines  of  rails  appear  to  meet  off  in  the  distance.  So 
it  is  with  any  set  of  parallel  lines;  if  the  eye  follows 
them  for  a  distance— and,  when  speaking  geometric- 


Fig.  2 

ally,  we  give  this  distance  a  value  of  infinity — they 
all  appear  to  meet  in  one  point.  This  point  we  call 
their  vanishing  point.  When  our  line  of  sight  follows  out 
these  parallel  lines  to  infinity,  where  they  appear  to  meet, 
for  all  practical  purposes  the  line  of  sight  is  parallel  to 
the  given  set  of  lines.  Reference  to  Fig.  2  may  serve 
to  make  this  explanation  clearer.  Point  S  represents 
the  position  of  the  eye.  A  cube  BD  rests  on  a  horizontal 


154  MECHANICAL  DRAFTING. 

plane  on  the  other  side  of  the  picture  plane.  The  four 
parallel  edges,  AB,  CE,  etc.,  of  the  cube  are  produced  as 
indicated  by  dotted  lines  to  the  right;  if  they  are  pro- 
duced an  infinite  distance  they  will  appear  to  meet,  and 
the  line  of  sight  from  S  to  the  apparent  meeting  or 
vanishing  point  is  the  line  thru  S  and  V.  Then,  as  ex- 
plained above,  if  SV  meets  AB,  CE,  etc.,  at  infinity,  it 
is  parallel  to  them.  But  AB,  CE,  etc.,  are  perpendicular 
to  the  picture  plane;  therefore  the  line  thru  S  and  V  out 
to  this  vanishing  point  is  also  perpendicular  to  the  pic- 
ture plane  and  must  pass  thru  s',  the  projection  of  S  on 
the  picture  plane.  As  viewed  from  point  S,  the  four 
edges,  AB,  CE,  etc.,  which  we  have  produced  to  infinity, 
do  not  in  reality  appear  to  be  parallel  lines  forming  the 
edges  of  a  long  prism,  but  seem  to  represent  the  four 
edges  of  a  long  pyramid.  To  return  to  the  perspective, 
suppose  we  wish  to  represent  this  long  pyramid  on  the 
picture  plane  as  seen  from  S.  According  to  Art.  97, 
lines  are  drawn  from  S  to  the  several  points  of  the 
pyramid;  the  line  from  S  to  the  imaginary  apex  at  in- 
finity pierces  the  picture  plane  at  s';  and  the  lines  from 
S  to  A,  C,  D,  and  F  pierce  the  picture  plane  at  «i  Ci  d^  fl ; 
then  &!  Ci  di  /i  -s'  is  the  perspective  of  the  pyramid.  From 
this  explanation  it  is  seen  that  the  perspective  of  all  lines 
perpendicular  to  the  picture  plane  meet  at  s',  the  vertical 
projection  of  the  point  of  sight.  For  this  reason  s'  is 
called  the  vanishing  point  of  perpendiculars.  The  fact 
that  perpendiculars  do  converge  at  s'  affords  an  easy 
method  of  constructing  the  perspective  of  any  object 
when  placed  in  a  certain  position.  Lines  from  S  to  the 
other  points  of  the  cube  are  seen  to  pierce  the  picture 
plane  in  points  on  the  perspectives  of  these  perpendicu- 
lars, giving  the  figure  bt  Oi  Ci  d^  /i  glt  This  figure  repre- 


PERSPECTIVE. 


155 


sents  the  cube  as  seen  from  S.    Face  ABEC  is  not  visible 
from  S. 

THE  HORIZON  IN  PERSPECTIVE 

(102)  Any  line  which  is  perpendicular  to  a  vertical 
plane  is  horizontal.  In  Fig.  2  the  lines  AB,  CE,  etc.,  are 
horizontal  lines  and,  when  produced  an  infinite  distance, 


appear  to  meet  in  a  point  on  what  we  commonly  call  the 
horizon.  Then  the  line  of  sight  from  S  to  this  meeting 
point  becomes  a  horizontal  line,  and  the  perspective  of 
the  horizon  will  be  the  horizontal  line  drawn  thru  the 
point  s'.  The  horizontal  line  lying  in  the  picture  plane 


156  MECHANICAL  DRAFTING. 

and  passing  thru  the  vertical  projections  of  the  point  of 
sight,  s',  is  also  called  the  horizon. 

SPECIAL  POSITION  OF  THE  OBJECT 

(103)  If  the  cube  in  Fig.  2  be  moved  until  face  ACDF 
coincides  with  the  picture  plane,  then  this  face  becomes 
its  own  perspective  and  each  line  on  this  face  is  shown 
in  its  true  value ;  i.  e.,  a  circle  shows  as  a  true  circle,  etc. 
From  this  it  follows  that  the  perspective  of  any  circle 
whose  plane  is  parallel  to  the  picture  plane  will  be  a  true 
circle;  its  diameter  will  be  less  or  greater  than  the  true 
diameter,  however. 

MECHANICAL  CONSTRUCTION  OF  A  PERSPECTIVE 

(104)  Inasmuch  as  all  lines  in  perspective  are  shorter 
than  the  lines  which  they  represent,  except  in  the  case  of 
lines  which  lie  in  the  picture  plane,  it  will  be  best  to  put 
one  face  of  the  object  or  one  face  of  a  circumscribed 
parallelepiped  into  coincidence  with  the  picture  plane,  in 
order  that  we  may  have  a  foundation  of  actual  measure- 
ments on  which  to  base  our  construction. 

COORDINATES 

(105)  The  position  of  the  point  of  sight  with  respect 
to  some  chosen  point,  A,  of  the  object  will  hereafter  be 
given  as  follows: 

x  =  distance  of  point  of  sight  to  right  or  left  of  A 
as  x  is  +  or  — . 

y  =  distance  of  point  of  sight  above  or  below  A  as  y 
is  +  or  — . 

z  =  distance  of  point  of  sight  before  the  point  A; 
e.  g.,  x  =  3",  y=  -  4",  z  =  6"  locates  S  3"  to  the  right 
and  4"  below  A  and  6"  before  the  picture  plane. 


PERSPECTIVE. 


157 


(106)  Problems.  To  draw  the  perspective  of  a  cube 
114"  on  edge,  one  face  of  the  cube  coinciding  with  the 
picture  plane ;  x  =  — 2",  y  =  1",  z  =  4".  A  is  taken  at 
corner  A. 


Fig.  3 


Construction.    See  Fig.  3. 

Draw  well  toward  the  top  of  the  sheet  a  horizontal  line 
G.  L.,  the  intersection  of  the  horizontal  and  vertical 
planes.  Since  the  picture  plane  coincides  with  the  verti- 
cal plane  this  line,  G.  L.,  represents  the  picture  plane  as 


158  MECHANICAL  DRAFTING. 

seen  from  the  top.  Construct  in  a  convenient  position  the 
top  view  b-fc-da-gj  of  the  cube,  the  line  da-fc,  which  repre- 
sents the  front  face  of  the  cube,  coinciding  with  G.  L.  At 
any  desired  distance  directly  below  the  top  view,  draw  the 
square  ajid  di  which  is  the  front  view  of  the  cube. 

The  point  of  sight  S  is  to  be  located  by  the  three  co- 
ordinates given  with  reference  to  the  point  A  on  the  cube. 
First,  locate  S  as  viewed  from  above.  The  top  view  of  S 
(lettered  s)  is  2"  to  the  left  of  a  (x  =  —2)  and  4"  in  front 
of  a  (z=4").  The  square  b-fc-da-gj,  G.  L.,  and  s  now 
represent  respectively  the  cube,  the  picture  plane,  and  the 
point  of  sight  as  they  appear  looking  down  from  above. 
Second,  locate  S  as  viewed  from  the  front.  The  front 
view  of  S  (lettered  s')  is  V  to  the  left  of  a,  (x  =  -2)  and 
V  above  a^  (y=l").  The  square  ttif^ddi  and  s'  now  rep- 
resent respectively  the  cube  and  the  point  of  sight  as 
viewed  from  the  front. 

The  square  ajiddi  is  the  perspective  of  the  front  face 
of  the  cube  since  this  face  lies  in  the  picture  plane.  Draw 
lines  from  a^  flt  d,  and  di  to  s'.  This  figure  s'  —  aif^ddi 
then  is  the  perspective  of  the  long  pyramid  spoken  of  in 
Art.  101.  The  perspectives  of  the  edges  of  the  cube  that 
are  perpendicular  to  the  picture  plane  will  lie  along  these 
lines  just  drawn  to  s'.  For  example,  the  perspective  of 
the  edge  AG  is  a^i,  lying  along  a^  s'  and  it  is  only  neces- 
sary to  locate  0i  on  this  line.  To  locate  glt  draw  sg  and 
where  it  crosses  G.  L.  at  v  drop  a  perpendicular  to  G.  L. 
until  it  intersects  aa  s'.  Since  sj  coincides  with  sg,  j^  will 
lie  directly  below  g:  on  drf'  and  the  perspective  of  the  left 
side  of  the  cube  is  completed  as  a^gijidi.  A  horizontal  line 
from  #1  produced  until  it  interesects  /is',  completes  the 
perspective  of  the  cube.  It  is  easily  seen  that  sg  is  the 


PERSPECTIVE.  159 

top  view  of  a  line  of  sight  from  S  to  G  and  was  drawn  to 
ascertain  the  distance  v d  to  the  left  of  the  edge  FD  of  the 
cube  at  which  the  line  of  sight  pierces  the  picture  plane. 

It  is  desired  to  place  a  small  pyramid  on  top  of  the 
cube,  the  edges  of  its  base  parallel  to  the  edges  of  the  cube 
and  its  apex  P  directly  above  the  center  of  the  top  face. 
Construct  the  top  and  front  views  of  the  pyramid  in  place 
and  proceed  with  the  construction  of  the  perspective  of 
the  base  as  shown.  The  perspective  pi  of  the  apex  is  the 
point  in  which  the  line  of  sight  sp  pierces  the  picture 
plane  and  is  found  by  dropping  a  perpendicular  from  the 
point  where  sp  crosses  G.  L.  until  it  meets  s'  p'.  The  per- 
spective of  the  pyramid  is  then  readily  completed. 

In  certain  instances,  a  left  side  view  will  be  an  addi- 
tional aid  in  constructing  the  perspective.  In  Fig.  3,  the 
square  V'g"— fa"  —  tt'cf'  — j",  G^  L^  and  s"  represent 
respectively  the  cube,  the  picture  plane  and  the  point  of 
sight  as  viewed  from  the  left.  The  line  s"p"  represents 
the  line  of  sight  from  s  to  the  apex  p  of  the  small  pyramid 
as  viewed  from  the  left  and  a  horizontal  line  drawn  from 
v"  meets  s'p'  at  plm  It  will  be  readily  seen  that  the  per- 
spective could  have  been  determined  from  the  left  side 
and  front  views  without  the  use  of  the  top  view  at  all. 
The  use  of  both  top  and  left  side  views  is  usually  unneces- 
sary. 

CIRCLES  IN  PERSPECTIVE 

(107)  The  8  point  method  may  be  used  in  construct- 
ing circles  in  perspective.  This  is  illustrated  on  the  cube 
in  Fig.  3.  The  diagonals  can  easily  be  drawn  and  the 
points  of  tangency  of  the  perspective  with  the  upper  and 
lower  lines  /j  g^  and  dj_  jl  determined  by  drawing  a  ver- 
tical line  thru  the  intersection  of  the  diagonals. 


160  MECHANICAL  DRAFTING. 

IRREGULARLY  SHAPED  OBJECTS 

(108)  Any  irregularly  shaped  object  may  be  easily 
drawn  in  perspective  by  first  enclosing  the  object  in  a 
parallelepiped  and  referring  the  several  constructions 
of  the  object  to  lines  of  the  parallelepiped. 

POSITION  OF  POINT  OF  SIGHT 

(109)  Considerable  care  and  judgment  must  be  used 
in  placing  the  point  of  sight,  for  it  is  easily  understood 
that  a  house  viewed  from  a  point  only  two  feet  in  front 
of  it  would  look  absurd;  however,  its  perspective  can  be 
constructed  as  easily  under  such  circumstances  as  any 
other.    It  is  well  to  estimate  approximately  from  what 
particular  position  we  would  likely  view  that  object  to 
obtain  the  best  view,  taking  into  account  the  size  of  the 
object  in  this  estimate.    The  point  of  sight  may  then  be 
placed  accordingly.    For  large  objects  a  safe  rule  is  to 
place  the  point  of  sight  in  front  of  the  object  a  distance 
equal   to   twice   the   greatest   dimension.     For   smaller 
objects  we  may  increase  this  to  4  or  5  times  the  greatest 
dimension. 


APPENDIX 


162  MECHANICAL  DRAFTING. 

PHOTOGRAPHIC  REPRODUCTIONS 

Blueprinting.  Blueprinting  is  in  short  a  process  of 
simple  photographic  reproduction  on  sensitized  paper, 
of  drawings  which  have  been  made  on  some  translucent 
material;  this  material  may  be  tracing  cloth,  tracing 
paper,  or  ordinary  paper  oiled  after  the  drawing  has 
been  finished.  In  common  practice  the  process  is  some- 
what rough  as  one  would  infer  from  a  glance  at  the 
average  print;  however,  with  care  it  can  be  carried 
nearly  to  the  same  limits  of  refinement  as  other  photo- 
graphic printing. 

BLUEPRINT  PAPERS 

Occasions  may  arise  when  it  is  necessary  to  sensitize 
paper  for  blueprinting;  however,  unless  absolutely  nec- 
essary no  draftsman  should  ever  bother  to  coat  his  own 
paper,  for  it  is  a  tedious  and  most  unsatisfactory  proc- 
ess. The  machine-coated  papers  sold  by  any  of  the  in- 
strument companies  in  10  or  50-yard  rolls  of  any  width 
and  of  any  desired  thickness  or  quality  of  paper  is 
cheap,  keeps  well  for  months  in  a  tin  tube,  and  always 
gives  better  results  than  paper  coated  by  the  amateur. 
For  prints  which  must  stand  extra  hard  use,  either 
mounted  paper  (cloth-backed  paper)  or  blueprint  cloth 
(a  smooth,  hard-surfaced,  sensitized  cloth)  should  be 
used;  the  latter,  however,  seldom  gives  the  sharp  detail 
obtainable  on  paper.  Below  is  tabulated  information 
that  will  be  of  value  in  ordering  papers  or  cloth. 


APPENDIX. 


163 


Blue  Print  Paper  and  Cloth 


PAPER 

CLOTH 

WEIGHT 

USE 

WEIGHT 

USE 

Extra  thin 

For  sending  thru  mail. 
Not    satisfactory    for 
shop  use,  too  thin. 

Extra  thin 

L<arge  prints  which 
are  to  receive  extra 
hard  wear. 

Thin 

For  large  prints  that 
would  be  too  bulky  on 
heavier  paper. 

Medium 

Small  maps,  moderate 
sized  prints  that  re- 
ceive extra  wear. 

Medium 
thick 

Best  for  all  ordinary  use,  shop,  construction  work,  etc. 

Thick 


For  durable  small  prints;  maps,  land  plots,  etc. 


Printing  Speed  in  Bright  Sunlight 


Regular 

Rapid 

Extra  Rapid 

Elec.  Rapid 

4  min. 

2  min. 

40  sec. 

25  sec. 

In  ordering  paper  be  sure  to  state  the  printing  speed  desired; 
e.  g.,  1  roll;  50  yds.  x  36  in.,  Extra  Thin,  Electric  Rapid,  Blue  Print 
Paper. 

TO  SENSITIZE  PAPER 

Paper.  Only  "unsized"  and  well-washed  papers  are 
suitable  for  blueprinting.  The  size  used  on  many  papers 
to  give  it  a  glossy  and  easy  writing  surface  discolors  the 
blueprint  solution  immediately.  Likewise  paper  from 
which  the  sulphur,  used  in  its  manufacture,  has  not  been 
well  washed  will  discolor.  Practically  any  unsized 
"bond"  or  "parchment"  paper  will  be  found  satisfac- 
tory for  printing. 

Solution.  The  formula  in  most  common  use  for  the 
sensitizing  solution  is:  (1)  Bed  prussiate  of  potash,  1 
oz. ;  water  (distilled),  4  oz. ;  (2)  double  citrate  of  iron 
and  ammonia,  1  oz. ;  water  (distilled),  4  oz.  As  long  as 


164  MECHANICAL  DRAFTING. 

these  solutions  are  kept  separate  sunlight  has  no  effect 
upon  them.  However,  the  second  solution  should  be 
kept  in  a  well  stoppered  bottle  of  dark  colored  glass. 

To  sensitize  the  paper,  mix  equal  volumes  of  the 
above  solutions  and  apply  either  with  a  camel's  hair 
brush,  brushing  first  horizontally,  then  vertically,  to 
insure  even  coating,  or  float  the  paper  for  a  few  seconds 
in  a  shallow  granite  pan  partially  filled  with  the  solu- 
tion, and  hang  by  one  corner  to  dry.  This  sensitizing 
must  of  course  be  done  in  a  dark  room.  If  the  solution 
of  citrate  of  iron  is  kept  too  long  it  may  mold  and  spoil ; 
hence,  as  the  crystals  dissolve  quite  readily  it  may  be 
best  to  make  this  solution  only  when  it  is  to  be  used  and 
then  only  what  is  needed.  The  bottle  in  which  the  citrate 
is  kept  should  be  glass  stoppered  to  prevent  moisture 
from  melting  down  the  crystals.  The  prussiate  does  not 
dissolve  so  readily  and  as  it  does  not  spoil  it  can  be  kept 
in  solution  in  any  quantity. 

VANDYKE  SOLAR  PAPER 

Vandyke  Solar  Paper,  sometimes  called  "Brown 
Print"  paper,  is  a  brown  paper  used  in  making  neg- 
atives for  positive  printing.  A  print  is  made  on  Van- 
dyke paper  from  a  tracing,  the  inked  side  of  the  tracing 
being  in  this  case  turned  to  the  paper,  so  that  a  reversed 
print  is  obtained.  The  lines  of  the  drawing  show  up 
white  on  a  deep  brown  background.  This  paper  is  then 
rubbed  with  oil  to  make  it  more  transparent  and  positive 
blueprints  are  made  from  it,  the  brown  side  of  the  nega- 
tive being  turned  toward  the  blueprint  paper.  In  this 
final  print  the  lines  of  the  drawing  show  up  blue  on  a 
white  background  instead  of  the  reverse  in  direct  print- 
ing from  the  tracing. 


APPENDIX.  165 

WASHING  AND  FIXING  VANDYKES 

Vandyke  paper  has  been  sufficiently  exposed  when 
the  surface  not  covered  by  the  black  lines  of  the  trac- 
ing has  turned  a  light  bronze  color.  After  washing 
for  a  few  minutes,  face  down  in  the  tank,  the  print  should 
be  fixed  with  a  solution  of  1  oz.  of  hyposulphite  of  soda 
to  1  qt.  of  water.  The  print  may  be  laid  on  a  board  and 
the  solution  applied  with  a  brush  or  better  still  the  print 
may  be  floated  face  down,  in  a  granite  pan  partially 
filled  with  the  hypo  solution ;  one  brushing  or  a  few  sec- 
onds floating  is  sufficient.  The  print  should  then  be 
washed  again  face  down,  to  remove  the  surplus  hypo. 

TO  TRANSPARENTIZE  VANDYKES 

It  is  possible  to  obtain  positive  prints  from  unoiled 
Vandykes;  however,  if  the  negative  has  been  rendered 
more  transparent  by  oiling  the  printing  time  will  be 
materially  reduced.  Any  clear  oil  or  white  grease 
will  answer  for  this  purpose,  white  tube  vaseline  being 
perhaps  the  most  convenient.  The  following  formula 
gives  a  transparentizing  oil  that  works  well:  4  oz. 
banana  oil,  lOc  tube  white  vaseline.  (Mix  the  two  by 
heating  slightly  and  keep  in  a  stoppered  bottle.)  The 
banana  oil  furnishes  a  quick  " drier"  and  the  vaseline  a 
permanent  oil.  If  there  is  much  transparentizing  to  be 
done  it  is  well  to  keep  a  ball  of  waste,  soaked  in  the 
above  solution,  in  a  covered  tin  can.  Never  apply  more 
grease  than  will  dry  in  a  few  minutes  and  be  sure  to 
oil  the  side  of  the  paper  which  is  to  be  turned  toward 
the  light.  Unless  necessary  never  use  paraffin  for  trans- 
parentizing; it  renders  the  paper  very  brittle  and  any 
wrinkles  in  a  paraffined  negative  show  plainly  on  the 
print. 


166  MECHANICAL  DRAFTING. 

POSITIVES  ON  OLD  VANDYKE  PAPER 

In  making  positive  prints  on  old  Vandyke  paper 
some  little  care  must  be  exercised.  When  printed  and 
washed  the  unexposed  or  white  parts  turn  decidedly 
yellow;  this  can  be  prevented  if  -the  print  is  merely 
dipped  in  the  water  to  wet  the  surface  and  start  the 
printing  out  and  immediately  floated  on  the  fixer;  the 
fixer  will  print  out  the  lines  and  prevent  the  background 
from  turning  yellow.  These  precautions  are  not  neces- 
sary in  making  negatives  on  old  paper,  for  tho  unexposed 
parts  may  turn  yellow  the  negative  will  print  well  when 
oiled. 

BLUEPRINTING  FROM  TYPEWRITTEN  SHEETS 

To  obtain  clear  sharp  prints  from  typewritten  sheets 
a  moderately  thin  hard  surfaced  paper  and  new  black 
typewriter  ribbon  should  be  used.  If  there  is  much 
work  to  be  done  it  will  be  well  to  obtain  an  extra 
heavily  inked  ribbon.  In  typewriting  place  under  the 
the  paper  a  sheet  of  black  carbon  paper  with  carbon  face 
toward  the  paper;  thus  an  impression  is  obtained  on  both 
sides  of  the  paper.  Use  each  sheet  of  carbon  paper  only 
once  for  this  purpose. 

In  oiling,  one  may  not  rub  these  sheets,  as  the  carbon 
will  smear.  Instead,  lay  over  the  typewritten  sheet  a 
square  of  oily  cotton  flannel,  then  a  sheet  of  heavy  paper 
and  roll  with  a  small  picture  mounting  roll.  Or  better, 
if  time  permits,  lay  pieces  of  oily  cotton  cloth  between 
the  sheets  and  weight  down  with  a  heavy  book  for  sev- 
eral hours.  Arrange  sheets  and  cloth  as  follows :  Paper, 
cloth,  two  sheets  of  paper,  cloth,  two  sheets  of  paper, 
cloth,  etc.  In  printing  from  these  sheets,  over  expose 
the  paper  slightly  and  wash  in  water  to  which  hydrogen 


APPENDIX.  167 

peroxide  has  been  added  in  the  proportion  of  y2  tea- 
spoonful  to  2  gallons  water;  the  hydrogen  peroxide  will 
bring  out  the  over  exposed  parts  and  deepen  the  blue. 
The  above  solution  can  be  used  to  advantage  in  washing 
any  blueprints;  a  sharper  contrast  between  the  white 
lines  and  blue  background  can  be  obtained. 

PRINTING  FROM  OLD  BLUEPRINTS 
Occasionally  reproductions  of  drawings  are  wanted 
when  the  tracings  are  not  available.  By  use  of  the 
" Direct  Copier"  of  the  Frederick  Post  Co.,  Chicago, 
an  old  blueprint  may  be  rendered  sufficiently  dense  to  act 
as  a  good  negative.  This  " Direct  Copier"  consists  of 
two  concentrating  solutions  to  be  applied  to  the  old  blue- 
print to  deepen  the  blue;  the  transparentizing  oil  must 
then  be  used  to  clear  up  the  white  lines.  If  the  ''Direct 
Copier"  is  not  available  and  there  is  not  sufficient  time 
for  a  tracing  a  fairly  good  positive  may  be  made  from  a 
blueprint  by  merely  transparentizing  it. 

PRINTING  FROM  HEAVY  CARDBOARD 
If  it  is  desired  to  make  a  blueprint  of  a  drawing 
mounted  or  printed  on  heavy  cardboard  or  of  a  draw- 
ing on  mounted  paper,  the  face  of  the  drawing  should 
be  soaked  with  alcohol  and  immediately  clamped  in 
the  printing-frame.  The  alcohol  will  not  evaporate 
while  closed  in  the  frame  nor  will  it  dissolve  the  blue- 
print solution  if  it  should  soak  thru  the  cardboard.  The 
length  of  time  required  for  printing  will  have  to  be 
learned  from  experiment. 

PRINTING  FROM  COORDINATE  PAPER 
Coordinate  paper  printed  in  red  gives  better  blue- 
prints than  the  paper  printed  in  blue  or  green.    Always 


168  MECHANICAL  DRAFTING 

transparentize  the  coordinate  paper  before  printing ;  it 
will  save  time  in  printing  and  give  better  results. 

Positive  blueprinting  of  typewritten  sheets.  Excel- 
lent negatives  for  positive  printing  of  typewritten 
sheets  may  be  made  from  new  black  carbon  paper  as  fol- 
lows :  Eemove  the  ribbon  from  the  typewriter  and  place 
the  carbon  paper  in  the  machine,  face  up,  with  a  sheet  of 
thin  hard  surfaced  paper  over  it.  A  reversed  impres- 
sion will  of  course  be  obtained  on  the  back  of  this  sheet 
of  paper  and  the  better  the  quality  of  paper  the  more 
clear  cut  will  be  the  letters  on  the  carbon  sheet.  The 
reason  for  placing  the  carbon  with  face  to  the  ,cover  sheet 
is  to  obtain  such  an  impression  as  to  make  it  possible  to 
place  the  carbon  side  of  the  paper  toward  the  glass  of 
the  printing  frame  instead  of  toward  the  blueprint  paper. 

Handle  the  carbon  paper  very  carefully;  a  finger 
mark  or  smudge  may  easily  ruin  the  negative. 

The  time  for  printing  will  have  to  be  determined  by 
experiment ;  it  should  be  somewhat  longer  than  for  print- 
ing from  tracings. 


APPENDIX.  169 


LINE  ENGRAVING  ON  ZINC 

Process.  Line  engraving  on  zinc  is  essentially  an 
etching  process  and  the  procedure  is  as  follows :  A  glass 
plate  is  coated  with  a  sensitive  solution  and  a  negative 
made  thereon,  by  the  use  of  a  camera,  from  the  drawing 
submitted.  After  development  the  film  negative  is 
removed  from  the  glass  plate  and  transferred  to  another 
glass  plate  in  a  reverse  position,  thereby  converting  it 
into  a  positive  film.  A  second  negative  is  now  obtained 
upon  the  sensitized  surface  of  a  polished  zinc  plate.  A 
compound  composed  largely  of  printer's  ink  and  grease 
is  applied  to  the  surface  of  this  negative.  This  coating 
adheres  to  the  portions  corresponding  to  the  lines  of  the 
drawing  and  when  the  plate  of  zinc  is  immersed  in  acid 
the  surface  is  eaten  away  except  where  protected  by  the 
ink  and  grease  compound.  The  result  is  a  duplicate  on 
the  zinc  plate  of  the  original  drawing. 

Drawings.  In  order  that  one  may  secure  the  best 
possible  line  engraving  on  zinc  especial  care  should  be 
taken  with  the  drawing.  The  paper  used  should  be  either 
white  or  bluish  white;  ordinary  drawing  paper,  tracing 
cloth,  or  transparent  vellum  may  be  used.  Very  black 
water  proof  drawing  ink  should  be  used  in  making  the 
lines,  and  care  should  be  exercised  that  in  erasing,  the 
black  lines  are  not  dulled.  If  any  parts  of  the  lines  are 
faded  from  erasing,  they  are  not  photographed  sharply 
and  the  resulting  lines  may  be  somewhat  ragged.  So  far 
the  best  ink  that  the  writer  has  found  for  this  purpose 
is  the  United  States  Blue  Print  Paper  Company's  Draw- 
ing Ink. 


170  MECHANICAL  DRAFTING. 

Reduction.  In  making  a  drawing  for  etching,  it  is 
best  to  make  it  of  such  a  size  that  when  reduced  to  one- 
half  or  one-third  of  its  dimensions,  it  will  be  of  the  desired 
size  for  use ;  that  is,  if  a  diagram  is  finally  to  be  4  x  6 
inches, the  drawing  had  better  be  made  about  8x12  inches. 
It  should  be  remembered,  however,  that  very  fine  lines 
do  not  reduce  in  the  same  proportion  as  heavy  lines.  To 
prevent  very  fine  lines  from  disappearing  entirely,  the 
engraver  will  have  to  use  methods  which  perhaps  will 
increase  them,  and  quite  likely  this  increase  will  not  be 
uniform,  so  that  in  making  up  a  drawing  care  should  be 
taken  to  make  the  lines  about  twice  the  desired  final 
weight.  For  purposes  of  illustration  hidden  lines  should 
be  omitted  and  dimension  lines  should  be  made  of  sec- 
ondary importance.  Likewise,  shading  will  be  found  use- 
ful in  adding  to  the  appearance  of  a  drawing.  For  best 
appearance  it  is  better  to  use  printed  letters  than  free- 
hand. This  may  be  done  by  having  all  material  which  is 
to  go  on  the  drawing  set  up  in  type  in  a  size  about  twice 
that  finally  desired,  printing  it  on  gummed  paper,  and 
pasting  this  material  on  the  original  drawing.  Any  lines 
which  may  be  placed  on  the  original  drawing,  and  which 
are  later  found  unnecessary  or  incorrect,  may  be  simply 
marked  over  by  the  draftsman,  with  the  understanding 
that  the  engraver  is  to  paint  them  out;  the  only  rigid 
requirements  are  that  all  lines  be  sharp,  a  dense  black, 
and  that  the  paper  used  be  white. 


APPENDIX.  171 

WAX  ENGRAVING  PROCESS 

Wherever  it  is  impossible  to  submit  a  high  grade  line 
drawing  from  which  to  make  the  zinc  line  engraving,  an 
accurate  pencil  or  ink  drawing  or  blue  print  may  be  sub- 
mitted to  any  of  the  companies  handling  wax  engraving 
work.  This  drawing  or  print  is  photographed  on  the  sen- 
sitized wax  surface  of  a  copper  plate.  The  photographed 
outlines  are  then  scratched  through  the  wax  to  the  copper 
plate  with  appropriate  tools.  All  necessary  lettering  is 
set  in  type  and  pressed  into  the  softened  wax.  This  wax 
engraving  is  then  electrotyped,  backed  with  type  metal 
and  mounted  on  a  wooden  block.  Very  clean  cut  legible 
lines  result  from  this  process,  and  it  seems  to  be  used 
very  largely  in  making  cuts  of  diagrams,  curves,  text 
book  illustrations,  etc. 

A  slight  modification  of  this  process  is  to  make  the 
drawing  directly  on  the  waxed  covering  of  a  copper  plate, 
omitting  the  photographing  process.  The  lines  of  the 
drawing  are  then  scratched  through  to  the  copper  plate 
and  the  procedure  is  as  before.  This  scheme  of  engrav- 
ing is  very  expensive,  and  perhaps  will  not  be  found 
profitable  except  as  noted  before  in  making  cuts  of  charts, 
diagrams,  curves,  etc.,  on  which  a  high  degree  of  accuracy 
is  desired. 

HALF  TONES 

The  half  tone  is  the  cut  usually  used  in  reproductions 
of  photographs,  wash  or  charcoal  drawings,  etc.  It  is 
perhaps  unnecessary  to  explain  in  detail  the  process.  It 
will  be  better  to  give  some  suggestions  on  the  difficulties 
that  may  be  encountered. 


172  .   MECHANICAL  DRAFTING. 

Drawings.  It  should  be  remembered  always  that 
when  a  half  tone  is  to  be  made  from  a  photograph,  wash 
drawing,  or  drawing  of  any  other  description,  that  abso- 
lutely everything  that  can  be  seen  by  the  eye  on  the  orig- 
inal drawing  or  photograph,  will  likewise  be  seen  and 
reproduced  by  the  eye  of  the  camera.  It  requires  ex- 
tremely careful  work  to  paint  out  by  the  use  of  an  air 
brush  any  lines  which  have  been  put  in  by  mistake,  and 
such  work  should  be  left  to  the  engraver.  It  is  possible 
to  secure  copies  of  high  grade  half  tones  which  one  may 
find  in  magazines,  etc.,  by  very  carefully  cutting  out  such 
half  tones,  trimming  them  very  neatly,  and  pasting  them 
on  a  background  of  white  paper.  Extreme  care  must  like- 
wise be  exercised  in  pasting  down  such  cuts  that  the  back- 
ground is  not  smudged  by  glue  which  may  run  from  under 
the  drawing,  or  by  soiled  fingers.  The  camera  will  surely 
see  everything  that  can  be  seen  by  the  eye. 

Photographs.  The  type  of  photograph  which  seems 
to  work  best  in  the  half  tone  process  is  that  which  is  made 
on  a  glazed  paper.  If  any  great  amount  of  work  is  to  be 
made  from  photographs  it  will  perhaps  be  better  to  con- 
sult with  some  good  engraver  for  his  advice  on  the  kind 
of  prints  that  he  desires. 


APPENDIX. 


173 


ABBREVIATIONS 

METALS 

Aluminum  

Almn. 

Babbitt   

Bb. 

Brass  .         

B. 

Bronze     

Bz. 

Carbon         

Cbn. 

Cast  brass      

C.  B. 

C.  Cop. 

Cast  Iron         

c.  i  P 

Cast  steel    

C.  S. 

Cold  rolled  steel    

C.  R.  S. 

Copper         

Cop. 

Lead        

Lead 

Malleable  iron    

M.I. 

Open  hearth  steel           

O.  H.  S. 

Phosphor  bronze         ..... 

Ph.  Bz. 

Steel        

Steel. 

Steel  casting       

S.  C. 

W    I. 

Zinc      

Zn. 

Tool  steel        

T    S. 

Forged  tool  steel        .         .         . 

F.  T.  S. 

High  speed  steel            ..... 

H.  S.  S. 

GAGES 

Brown  &  Sharpe,  or  American  Standard 

Wire  Gage      

B.  &  S. 

Birmingham,  or  Stubs  Iron  Wire  Gage 

B.  W.  G. 

National,  or  Roebling's,  or  Washburn  & 

Moen's    

N.  W.  G. 

Music  Wire  Gage           ..... 

M.  W.  G. 

United  States  Gage           .... 
Twist  Drill  &  Steel  Wire  Gage 

U.  S.  G. 
T.  D.  G. 

Stubs'  Steel  Wire  Gage     .... 

S.  W.  G. 

FASTENERS 


Button  head  bolt        .... 

Cap  screw 

Double  chamfered  hexagon  nut 

Eye  bolt 

Fillister  head  brass  machine  screw 
Fillister  head  iron  machine  screw 


Btn.  Hd.  B. 

Cap  Sc. 

Dbl.  Chmfd.  Hex.  Nut. 

EyeB. 

Fil.  Hd.  B.  M.  Sc. 

Fil.  Hd.  I.  M.  Sc. 


174  MECHANICAL  DRAFTING. 

Flat  head  wood  screw       ....  Flat  Hd.  Wd.  Sc. 

Flat  head  stove  bolt      ......  Flat  Hd.  Stove  B. 

Headless  set  screw Hdlss.  Set  Sc. 

Hexagon  nut Hex.  Nut. 

Lag  screw L,ag  Sc 

Machine  bolt Mach.  B. 

Machine  screw  nut M.  Sc.  Nut. 

Milled  body  tap  bolt M.  B.  Tap  B. 

Set  screw Set  Sc. 

Square  nut      . Sq.  Nut. 

Stud  bolt Stud  B. 

T-head  bolt     .  .  .  T-Hd.  B. 


WEIGHTS  AND  MEASURES,  ETC. 

Center Cr. 

Center  line C.  L,. 

Circumference Circum. 

Diameter dia.  or  D. 

Foot,  feet Ft.  or  ',  e.g.4' 

Horsepower    .         .         .         .         .         .         .  H.P. 

Inch,  inches In.  or  ".  e.g.4" 


MISCELLANEOUS 

Building Bldg. 

Case  harden C.H. 

Company Co. 

Counterbore Cbr. 

Countersink Csk. 

Cylinder Cyl. 

Drawing       .......  Dwg. 

General  .         .         .    •     .         .         .        .  Gnl. 

Hexagon Hex. 

Machine Mach. 

Manufacturing Mfg. 

Maximum        . Max. 

Minimum      .......  Min. 

Specification Spec. 

Square Sq. 

Standard Std. 

Threads Thds. 

Weight Wgt. 

Finish f. 


APPENDIX. 


175 


REFERENCE  TABLES 

KEY  FOE  THE  FOLLOWING  TABLES  OF  BOLTS,  NUTS,  ETC. 
A=0utside  Diameter  of  Threads  and  Thickness  of  Nut. 


B^Threads  per  Inch. 
C=Tap  Drill. 
D=Aeross  Flats. 
E=Across  Corners,  Hex. 
F=Across  Corners,  Sq. 
Gr=Thickness  of  Collar. 
H=Thickness  of  Head. 


I=Across  Flats. 

J=Thickness    Head    and 
Nut. 

K=Diameter  Collar. 

S=Width  of  Slot.— Deci- 
mals. 

X— Angle  of  Head. 


Hexagonal-Head  Cap-Screw 


1/4 


5/lo| 


38 


7/16|         1/2  |         9/16|         5  8  j 


3/4 


B    ]20 


J18 


16 


13 


J10_ 


7  16. 


1/2 


9  16| 


5/8 


S/4  |       13,  16|         7/8  | 


1-  1/i 


1/2  |       37/64]       41/64|       23/32|       55/64]       15/16]     1-1/641     1-5/32]  1-19/64 


Square-Head  Cap-Screw 


1/4 


5/16|         3/8  |         7/16|        1/2  | 


9  16 


5/8  |        3/4 


7/8 


B    20 


1 16 


10 


D 


38 


7/16] 


1/2 


9/16|        3/8  |      11/16 


3/4 


7/8  |  1-  1/8 


F   |       17/32]       39/64]       45/64 


51/64]        7/8  |      31  '32  |  1-  1/16  |  1-15/64]  1-19/32 


Iron  Set-Screw 


A     |  1/4  |       5  16  |       3.8  |       7/16  |       1/2  |       916  |       5/8  |       3/4  |     7/8 
B    |  20     |  18  |  16         ]  14  ]  13         |  12  11  10        |  9 


D    |  1/4  j       5/16  |       3  8  |       7/16  |      1/2 


9  16 


58 


3/4  I     7/8 


176 


MECHANICAL  DRAFTING. 


U.  S.  Standard  Bolts  and  Nuts 


Rough 


Finished 


J) 


E 


H 


1/4  |20         |10 


1/2  |      37/64|        7/10|        1/4  |        7/16| 


3/16 


5/16]  18 

1/4 

19/32]       11/16]       10/12]       19/64] 

17/32] 

1/4 

3/8  |16 

19/64]       11/16]       51/o4|       63/64]       11/32] 

5/8  | 

5/16 

7/16|14 

23/64|       25/32]         9/10]  1-  7/64]       25/64] 

23/32] 

3/8 

1/2  |13 

13/32]         7/8  |                 |  1-15/64]         7/16] 

13/16] 

7/16 

9/16|12 

15/32]       31/32]     -  1/8  |  1-23/64]       31/64] 

29/32| 

1/2 

5/8  |11 

33/64]     -  1/16]     -  7/32]  1-  1/2  |       17/32]  1             | 

9/16 

3/4 

10 

5/8 

-  1/4  |     -  7/16]  1-49/64]         5/8  | 

1-  3/16] 

11/16 

7/8 

9 

47/64]     -  7/16]     -21/32]  2-  I/  32]       23/32] 

1-  3/8  | 

13/16 

1 

8 

27/32 

-  5/8  |     -  7/8  |  2-19/64 

13/16] 

1-  9/16] 

15/16 

1-1/8 

7 

61/64]     -13/16]  2-  3/32]  2-  9/16]       29/32] 

1-  3/4  | 

1-  1/16 

1-1/4 

7 

1-  5/64|  2             |  2-  5/16]  2-53/64]  1             | 

1-15/16] 

1-  3/16 

1-3/8 

6 

1-11/64]  2-  3/16]  2-17/32]  3-  3/32]  1-  3/32] 

2-  1/8  ] 

1-  5/16 

1-1/2 

6 

1-19/64]  2-  3/8 

2-  3/4  |  3-23/64]  1-  3/16] 

2-  5/16] 

1-  7/16 

1-5/8 

5-1/2 

1-25/64]  2-  9/16 

2-31/32]  3-  5/8 

1-  9/32] 

2-  1/2 

1-  9/16 

1-3/4 

5 

1-  1/2 

2-  3/4 

3-  3/16]  3-57/64]  1-  3/8  | 

2-11/16 

1-11/16 

1-7/8 

5 

1-  5/8 

2-15/16 

3-13/32]  4-  5/32 

1-15/32] 

2-  7/8  j 

1-13/16 

2 

4-1/2 

1-23/32]  3-  1/8 

3-19/32]  4-27/64]  1-  9/16] 

3-  1/16] 

1-15/16 

2-1/4 

4-1/2 

1-31/32]  3-  1/2 

4-  1/32]  4-61/64]  1-  3/4  | 

3-  7/16] 

2-  3  16 

2-1/2 

4 

2-  3/16]  3-  7/8 

4-15/32]  5-31/64]  1-15/J6] 

3-13/16] 

2-  7/16 

2-3/4 

4 

2-  7/16]  4-  1/4 

4-29/32]  6 

2-  1/8  | 

4-  3   1(, 

2-11/16 

3 

3-1/2 

2^1/64]  4-  5/8 

5-11/32]  6-17/32]  2-  5/16] 

4-  9/16] 

2-15/16 

3-1/4 

3-1/2 

2-57/64]  5 

5-25/32]  7-  1/16|  2-  1/2  | 

4-15/16 

3-  3  16 

3-1/2 

3-1/4 

3-  1/8 

5-  3/8 

6-13/64]  7-39/64]  2-11/16] 

5-  5/16 

3-  7/16 

3-3/4 

3 

3-21/64]  5-  3/4 

6-  5/8  |  8-  1/8 

2-  7/8  | 

5-11/16J 

3-11/16 

4 

3 

3_37/64|  6-  1/8 

7-  1/16]  8-41/64]  3-  1/16] 

6-   1    16 

3-15/16 

4-1/4 

2-7/8]  3-13/16]  6-  1/2 

7-  1/2  |  9-  3/16]  3-  1/4  | 

6-  7/16] 

4-  3/16 

4-1/2 

2-3/4]  4-  3/64]  6-  7/8 

7-15/16]  9-  3/4 

3-  7/16] 

6-13/16] 

4-  7/16 

4-3/4 

2-5/8]  4-  9/32|  7-  1/4 

8-  3/8  |10-  1/4 

3-  5/8  | 

7-  3/16] 

4-11/16 

5 

2-1/2]  4-  1/2 

7-  5/8 

8-13/16]  10-49/64]  3-13/16] 

7-  9/16 

4-15/16 

5-1/4 

2-l/2|  4-  3/4 

8 

9-15/64|ll-  5/16]  4             ] 

7-15/16 

5-  3/16 

5-1/2 

2-3/8]  4-63/64]  8-  3/8 

9-ll/16|  11-27/32]  4-  3/16] 

8-  5/16 

5-  7/16 

5-3/4 

2-3/8]  5-15/641  8-  3/4  |10-  3/32|12-  3/8 

4-  3/8  | 

8-11/16 

5-11/16 

6 

2-1/4]  2-29/64 

9-  1/8  |10-17/32|  12-15/16]  4-  9/16] 

9-  1/16 

5-15/16 

APPENDIX. 


177 


^a 


ri 

^ 

o 

ro 

+. 

-* 

{^ 

s 

1 

s" 

I 

1 

! 

•o 

i 

i 

KJ 

s 

1 

0 

-l- 

VO 

^ 

o 

s 

1-1 

* 

lo 

^ 

2" 

X 

0 

0 

H 

. 

0 

« 

1 

X 

x"^ 

1 

1 

1 

= 

1 

3 

3 

1 

a 

1 

§ 

13 

X 



FT 

— 

i 

w 

a 

§ 

1 

1 

8 

1 

1 

1 

I 

8 

I 

0 

I 

s? 

1 

i 



n 

9 

| 

S 

<S 

I 

i 

i 

rT 

s 

i 

- 

i 

^ 

M. 

q 

^ 

m 

Q 

09 

178 


MECHANICAL  DRAFTING. 


U.  S.  STANDARD  SCREW  THREADS. 


FORMULA 


p  =  pitch  =  — T7- 

I\o,  threads  per  inch 

d  =  depth  =  p  X  .6495 
f  =  flat  =     £- 

O 


Width  of  Flat. 

/4 

20 

.185 

.0063 

& 

18 

.2403 

.0069 

% 

16 

.2936 

.0078 

A 

14 

.3447 

.0089 

K2 

13 

.4001 

.0096 

12 

.4542 

.0104 

5x/ 

11 

.5069 

.0114 

M 

10 

.6201 

.0125 

% 

9 

.7307 

.0139 

1 

8 

.8376 

.0156 

IK 

7 

.9394 

.0179 

1/4 

7 

.0644 

.0179 

1% 

6 

.1585 

.0208 

114 

6 

.2835 

.0208 

1% 

5^/2 

.3888 

.0227 

1/4 

5 

.4902 

.0250 

iJi 

5 

.6152 

.0250 

2 

4/^ 

.7113 

.0278 

2/4 

4/^ 

.9613 

.0278 

2^ 

4  " 

2.1752 

.0313 

2% 

4 

2.4252 

.0313 

3 

3H 

2.6288 

.0357 

3/4 

3M 

2.8788 

.0357 

y/2 

3M 

3.1003 

.0385 

3M 

3 

3.3170 

.0417 

4 

3 

3.5670 

.0417 

4M 

2% 

3.7982 

.0435 

4H 

4.0276 

.0455 

4% 

2% 

4.2551 

.0476 

5 

2M 

4.4804 

.0500 

5/4 

2/^ 

4.7304 

.0500 

SH 

23^ 

4.9530 

.0526 

5M 

2% 

5.2030 

.0526 

6 

2M 

5.4226 

.0556 

APPENDIX. 


179 


FOR  TAPS  WITH  U.  S.  STANDARD  THREADS. 


Size 
of 
Tap. 

No. 
of 
Thds. 

Size  of      'Si 
Drill.      Tc 

7.e      No. 

Size 

Size 

No. 

Size 

Size 
of 
Tap. 

No. 
of 
Thds. 

Size 
D°i 

p.    Thds. 

Drill. 

Tap. 
1  14 

1*4 

2   f 

Thds 

Drill. 

I 

Hi 

A 

5/^ 

20 
18 
16 
14 
13 
12 
11 

V>>  in. 
15  in- 

ft       11 

H    10 

4      10 

v%    9 

H       9 
H       7 

% 
it 

S 

7 
6 
6 

5M 

5 

j| 

1|| 

l| 

4' 

4 

I 

Collar-Screw 

A|       I/ 

'8  | 

3/16|       I/ 

'4       5/16|       3/8  |     7/16]     1/2  |     9/16|     5/8 

3/4 

B|40 

|24 

|20 

|18         |16           [14 

|13         |12         |11         |10 

D|       1/8  | 

3/16|       1/4  |     5/16|       3/8  |     7/16|     1/2  |     9/16|     5/8 

3/4 

F|     ll/ 

64|     17/64|     11/32|     7/16|     17/32]  39/64)  11/16|  51/64|     7/8 

1-1/16 

K|       I/ 

'4  |     11/32|       7/16|     1/2  |      5/8  |  11/16|  15/16|  15/16|1 

1-1/4 

G|       1/32| 

3/64|       I/ 

16|     5/64]       3/32|     7/64|     1/8  |     9/64|     5/32|       3/16 

Pipe  Threads 

Diam. 

||      Thds.  Per  In. 

Diam.  Drill 

Diam.       |      Thds.  Per  In. 

Diam.  Drill 

1/8 

II 

27 

21/64 

1-1 

/4     |        11-1/2 

1-15/32 

1/4 

|| 

18 

29/64      ||      1-1/2 

11-1/2 

1-23/32 

3/8 

II 

18 

19/32      ||      2 

11-1/2 

2-  3/16 

1/2 

II 

14 

23/32      ||      2-1/2 

8 

2-11/16 

3/4 

|| 

14 

15/16      ||      3 

|          8                |      3-  5/16 

1 

|| 

11-1/2 

1-3/16      ||      3-1 

/2     |          8 

3-13/16 

Standard  taper  of  pipe  threads  is,  1  inch  in  16,  or  3/4  inch  to  1  foot. 


180 


MECHANICAL  DRAFTING. 


DECIMAL  EQUIVALENTS 

Of  8ths,  16ths,  32nds  and  64ths  of  an  inch 


8ths. 

&  =  .15625 

M  =  .234375 

&  =  .21875             ij  -  .265625 

H  =  -125 

A  =  .28125 

H  -  .296875 

M  =  -250 

JJ  =  .34375 

§i  =  .328125 

Y%  =  -375 

J§  =  .40625 

ft  =  .359375 

H  =  -500 

if  =  .46875 

ft  =  .390625 

%  =  .625 

ii  =  .53125 

ft  =  .421875 

M  =  -750 

M  =  .59375 

§|  =  .453125 

%  =  .875 

&  =  .65625 

ft  =  .484375 

§§  =  -71875 

ft  =  .515625 

16ths. 

§f  =  .78125 

ft  =  .546875 

&  =  .84375 

ft  =  .578125 

A  -  -0625 

§|  =  .90625 

ft  =  .609375 

A  =  -1875 

M  =  .96875 

ft  =  .640625 

A  =  -3125 

|f  =  .671875 

A  =  .4375 

$  =  .703125 

A  =  .5625 

64ths. 

$  =  .734375 

ft  =  -6875 

ft  =  .765625 

$  =  .8125 

A  =  -015625 

ft  =  .796875 

«  =  .9375 

A  =  .046875 

ft  =  .828125 

A  =  -078125 

ft  =  .859375 

32ds.- 

A  =  .109375 

ft  =  .890625 

A  =  .140625 

ft  =  .921875 

A  =  .03125 

ft  =  .171875 

ft  =  .953125 

A  =  .09375 

ft  =  .203125 

ft  =  .984375 

APPENDIX. 


181 


SIZES  OF  NUMBERS  OF  THE  U.  S.  STANDARD  GAGE. 


Number 
of   Gage. 

Approximate 
Thickness  in 
Fractions  of 
an  Inch. 

Approximate 
Thickness  in  Decimal 
Parts  of  an  Inch. 

Weight  per 
Square  Foot 
in  Ounces. 
Avoirdupois. 

Weight  per 
Square  Foot 
in  Pounds. 
Avoirdupois. 

16 

& 

.0625 

40 

2.5 

17 

ifff 

.05625 

36 

2.25 

18 

2ff 

.05 

32 

2. 

19 

TffTT 

.04375 

28 

.75 

20 

f0 

.0375 

24 

.50 

21 

TjVV 

.034375 

22 

.375 

22 

* 

.03125 

20 

.25 

23 

sfv 

.028125 

18 

.125 

24 

& 

.025 

16 

1. 

25 

?%v 

.021875 

14 

.875 

26 

jfl7 

.01875 

12 

.75 

27 

eVff 

.0171875 

11 

.6875 

28 

A 

.015625 

10 

.625 

29 

rf, 

.0140625 

9 

.5625 

30 

•i 

.0125 

8 

.5 

31 

vlv 

.0109375 

7 

.4375 

32 

TiftTJ 

.01015625 

6^ 

.40625 

33 

y|ff 

.009375 

6 

.375 

34 

iHff 

.00859375 

5M 

.34375 

35 

fffo 

.0078125 

5 

.3125 

36 

T^W 

.00703125 

4J^ 

.28125 

37 

sHu 

.006640625 

4M 

.265625 

38 

TffU 

.00625 

4 

.25 

182 


MECHANICAL  DRAFTING. 


DIFFERENT  STANDARDS  FOR  WIRE  GAGE. 


.  S 

1 

*o  & 

rt 

a** 

1   S 

cU;S 

_  & 

1 

li 

"!« 

1° 

£  s 

•£|& 

•|J? 

i°]s 

•-  2 

ss| 

11 

|| 

^  C/S 

Is 

"1  f 

3L- 

° 

W  c/3 

*%* 

* 

0 

000000 

.464 

46875 

000000 

00000 

.432 

j 

4375 

00000 

0000 

.46 

.454 

.3938 

.400 

.40625 

0000 

000 

.40964 

.425 

.3625 

.372 

.375 

000 

00 

.3648 

.38 

.3310 

.348 

.34375 

00 

0 

.32486 

.34 

.3065 

.324 

.3125 

0 

1 

.2893 

.3 

.2830 

.300 

.'227 

.28125 

1 

2 

.25763 

.284 

.2625 

.276 

.219 

.265625 

2 

3 

.22942 

.259 

.2437 

.252 

.212 

.25 

3 

4 

.20431 

.'238 

.2253 

.232 

.207 

.234375 

4 

5 

.18194 

.22 

.2070 

.212 

.204 

.21875 

5 

6 

.16202 

.203 

.1920 

.192 

.201 

.203125 

6 

7 

.14428 

.18 

.1770 

.176 

.199 

.1875 

7 

8 

.12849 

.165 

.1620 

.160 

.197 

.171875 

8 

9 

.11443 

.148 

.1483 

.144 

.194 

.15625 

9 

10 

.10189 

.134 

.1350 

.128 

.191 

.140625 

10 

11 

.090742 

.12 

.1205 

.116 

.188 

.125 

11 

12 

.080808 

.109 

.1055 

.104 

.185 

.109375 

12 

13 

.071961 

.095 

.0915 

.092 

.182 

.09375 

13 

14 

.064084 

.083 

.0800 

.080 

.180 

.078125 

14 

15 

.057068 

.072 

.0720 

.072 

.178 

.0708125 

15 

16 

.05082 

.065 

.0625 

.064 

.175 

.0625 

16 

17 

.045257 

.058 

.0540 

.056 

.172 

.05625 

17 

18 

040303 

.049 

.0475 

.048 

.168 

.05 

18 

19 

.03589 

.042 

.0410 

.040 

.164 

.04375 

19 

20 

031961 

.035 

.0348 

.036 

.161 

.0375 

20 

21 

.028462 

.032 

.03175 

.032 

.157 

.034375 

21 

22 

025347 

.028 

.0286 

.028 

.155 

.03125 

22 

23 

.022571 

.025. 

.0258 

.024 

.153 

.028125 

23 

24 

0201 

.022 

.0230 

.022 

.151 

.025 

24 

25 

.0179 

.02 

.0204 

.020 

.148 

.021875 

25 

26 

01594 

.018 

.0181 

.018 

.146 

.01875 

26 

27 

014195 

.016 

.0173 

.0164 

.143 

.0171875 

27 

28 

012641 

.014 

.0162 

.0149 

.139 

.015625 

28 

29 

011257 

.013 

.0150 

.0136 

.134 

.0140625 

29 

30 

010025 

.012 

.0140 

.0124 

.127 

.0125 

30 

31 

008928 

.01 

.0132 

.0116 

.120 

.0109375 

31 

32 

00795 

.009 

.0128 

.0108 

.115 

.01015625 

32 

33 

00708 

.008 

.0118 

.0100 

.112 

.009375. 

33 

34 

006304 

.007 

.0104 

.0092 

.110 

.00859375 

34 

35  • 

005614 

.005 

0095 

.0084 

.108 

.0078125 

35 

36 

.005 

004 

.0090 

.0076 

.106 

.00703125 

36 

37 

004453 

.0068 

.103 

.006640625 

37 

38 

003965 

.0060 

.101 

.00625 

38 

003531 

0052 

099 

39 

40 

003144 

.0048 

.097 

40 

APPENDIX.  183 

GEOMETRICAL   CONSTRUCTIONS 
THE  ELLIPSE 

Definition:  An  ellipse  is  a  curve  generated  by  the 
motion  of  a  point  which  moves  so  that  the  sum  of  its  dis- 
tances from  two  fixed  points  is  constant.  For  example, 
in  Fig.  1,  the  sum,  x  +  y,  of  the  distances  from  any  point 
0  on  the 'ellipse  to  the  two  fixed  points,  Fj  and  F2  is  con- 
stant and  equal  to  2a. 

Besides  being  considered  a  mathematical  curve  gen- 
erated according  to  a  certain  law,  the  ellipse  may  be 
considered  the  curve  which  is  cut  from  the  surface  of  a 
right  circular  cone  by  a  plane  which  intersects  all  of  the 
elements  and  is  oblique  to  the  axis.  Also  as  the  ortho- 
graphic projection  of  a  circle  which  is  oblique  to  the 
plane  of  projection. 

The  long  diameter  of  the  ellipse  is  known  as  the 
major  axis  and  the  short  diameter  as  the  minor  axis;  in 
analytic  geometry  these  axes  are  given  values  of  2a  and 
26,  Fig.  1. 

Construction.  The  ellipse  figures  so  prominently  in 
drafting  that  it  will  be  well  to  give  several  methods  of 
construction,  both  exact  and  approximate. 

Exact  Method.  (1)  From  the  law  according  to 
which  the  curve  is  generated  it  has  been  found  possible 
to  construct  the  ellipse  accurately  as  follows.  With 
point  0,  Fig.  2,  as  a  center  and  the  axes  as  diameters, 
describe  two  circles.  Then  from  0  draw  any  number  of 
radii  of  the  large  circle,  e.  g.,  OA,  OB,  OC,  OD,  etc. 
The  vertices  a,  b,  c,  d,  etc.,  of  the  right  angles  of  the 
right  triangles,  Aaa1}  Bbb^  etc.,  are  points  of  the  required 
ellipse  and  the  curve  may  be  traced  thru  these  points 
either  freehand  or  by  means  of  a  universal  curve. 


184 


MECHANICAL  DRAFTING. 


Fig.   2 


APPENDIX. 


185 


Fig.  4 


Pig.  6 


186  MECHANICAL  DRAFTING. 

Exact  method  (2)  Trammel  method.  If  from  any 
point  P,  Fig.  3,  on  the  edge  of  a  strip  of  paper  or 
ruler  the  semi  minor  and  semi  major  axes  be  measured 
to  points  b  and  a,  and  this  strip  or  ruler  placed  over  the 
axes  and  moved  so  that  point  b  is  always  on  the  major 
axis  and  a  on  the  minor  axis,  the  successive  positions  of 
point  P  are  points  of  the  required  ellipse.  These  posi- 
tions of  point  P  may  be  marked  with  a  pencil  or  needle 
point  and  the  ellipse  traced  thru  them. 

Approximate  method  (1)— 4  center  method.  Con- 
nect point  B,  Fig.  4,  with  point  A.  Then  with  0  as  a 
center  and  OB  as  a  radius  describe  the  arc  cutting  OA 
at  C;  lay  off  from  B,  on  BA,  the  distance  CA,  to  Cj. 
The  perpendicular  bisector  of  CiA  locates  two  of  the 
desired  centers  and  the  curve  may  be  drawn  with  the 
compass  as  shown. 

Approximate  method  (2)— 8  center  method.  Con- 
struction. Connect  points  A  and  B  and  draw  the  lines 
AE  and  BE,  Fig.  5.  Then  describe  the  quadrant  EC 
and  erect  the  perpendicular  CD.  From  point  0  in  which 
CD  intersects  AB  draw  OB.  The  arc  EF  locates  center 
No.  1.  EF  produced  locates  center  No.  3  at  K.  Con- 
nect D  and  K  and  produce  BF  to  J;  with  G  and  H  as 
centers  and  GJ  as  a  radius  describe  arcs  intersecting  at 
center  No.  2.  Centers,  4,  6,  and  8  may  then  be  located 
from  2.  It  will  be  noted  that  center  No.  2  does  not  lie 
on  the  radius  GK;  however,  it  is  so  small  a  distance 
from  GK  that  no  irregularity  can  be  detected  in  the 
curves  at  G. 


APPENDIX.  187 

THE  PARABOLA  AND  HYPERBOLA 


=  CP' 


Fig.  6 


188 

Parallel 


MECHANICAL  DRAFTING. 
TANGENT  CURVES  WITH  GIVEN  RADIUS 
Parallel 


Parallel 


Tangent  to  Two  Straight  Lines  Tangent  to  Straight  Line  and  Curve 


Y          iX_^T/ 


Through  a  Point  and  Tangent  to  a  Straight  Line     Through  a  Point  and  Tangent  to  a  Curve 
INTERSECTIONS 


Tfig.  7 


APPENDIX. 


189 


CONVENTIONAL  REPRESENTATIONS. 


1 


mg.  s 


190  MECHANICAL  DRAFTING. 

CONVENTIONAL  EEPKESENTATIONS  (Cont'd) 


Angle 


////////A 

Z-Bar 


fTTTTT// 

y77TT777\ 

H-Bar 
Pi«.  9 

APPENDIX.  191 

STANDARD    SYMBOLS    ADOPTED    BY    THE 

NATIONAL  CONTRACTORS7  ASSOCIA- 

TION AND  THE  AMERICAN  INSTI- 

TUTE OF  ARCHITECTS. 

YA^  Ceiling  outlet;   electric  only.    Numeral  in  center  indicates 

ySJ,  number  of  standard  16  c-p  incandescent  lamps. 


Ceiling  'outlet;  combination.    4/2  indicates  4-16  c-p  standard 
incandescent  lamps  and  2  gas  burners.    If  gas  only 


Hracket  outlet ;  electric  only.    Numeral  -in  center  indicates 
number  of  standard  16  c-p  incandescent  lamps. 


4— }?f —  -  Bracket  outlet ;  combination.    4/2  indicates  4-16  c-p  standard 

$     ;•<.  2-          incandescent  lamps  and  2  gas  burners.     If  gas  only  ^— Mf 

'A —  2  I  Wall'  or  baseboard  receptacle  outlet.    Numeral  in  center 

$     I — '  >  indicates  number  of  standard  16.  c-p  incandescent  lamps. 

M  Floor  outlet.     Numeral  in  center  indicates  number  of 

Standard  16  c-p  incandescent  lamps. . 


.       Outlet  for  outdoor  standard  or  pedestal  electric  only.   Numeral 
indicates  number  of  standard  16  c-p  incandescent  lamps. 


Outlet  for  outdoor  standard  or  pedestal;   combination.    6/3 
indicates  6  16  c-p.  standard  incandescent  lamps ;  3  gas  burners. 


Drop  cord  outlet. 

One-lamp  outlet,  for  lamp  receptacle. 

Arc  lamp  outlet. 


Special  outlet,  for  lighting,  heating  and  power-current,  as 
described  in  specifications. 


192  MECHANICAL  DRAFTING. 

ELECTEICAL  SYMBOLS  (Cont'd) 

Ceiling  fan  outlet. 

Distribution  panel 
Junction  or  pull  box. 


A£W  Motor  outlet 

[X]  Motor  control  outlet 

==\—F=-  Transformer. 


Main  or  feeder  run  concealed  under  floor. 
Main  or  feeder  run  concealed  under  floor  above. 
Main  or  feeder  run  exposed. 
Branch  circuit  run  concealed  under,  floor. 
Branch  circuit  run  concealed  under  floor  above. 
Branch  circuit  ran  exposed. 


— • « Pole  line. 

0  Riser. 

M  Telephone  outlet;   private  service. 

U  Telephone  outlet;  public  service. 

Q  Bell  outlet. 

(— u  Buzzer  outlet. 

Q2  Push  button  outlet.    Numeral  indicates  number  or  pushes., 

xgv  Annunciator.    Numeral  indicates  number  of  points. 

A  Speaking  tube. 


APPENDIX.  193 

ELECTEICAL  SYMBOLS  (Cont'd) 
^  Watchman  clock  outlet 

Watchman  station  outlet 

Master  time  clock  outlet 
Secondary  time  clock  outlet 


— © 


— 0) 


[Jj  Door  opener. 


B 


Special  outlet  for  signal  systems, 
as  described  in  specifications. 


Battery  outlet 

Circuit  for  clock,  telephone,  bell  or  other  service,  run  under 
floor,  concealed.  Kind  of  service  wanted  ascertained  by  symbol 
to  which  line  connects. 

Circuit  for  clock,  telephone,  bell  or  other  service,  run  under 
floor  above,  concealed.  Kind  of  service  wanted  ascertained  by 
symbol  to  which  line  connects.  Meter  outlet. 


194 


MECHANICAL  DRAFTING. 


SYMBOLS  USED  IN  REPRESENTING  ELEC- 
TRICAL AND  AUTOMOBILE 
CONSTRUCTION. 


-©- 


Head  Light  Side  Light 


Tail,  Dash  or  Instrument  Light 


D.  C.  Generator  Armature  and  Brushes 


M 


Motor  Armature  and  Brushes 


Coil—  Size  and  Weight  According  to  Us 


Condenser  Circuit 


APPENDIX. 


195 


ELECTEICAL  SYMBOLS  (Cont'd) 


A.  C.  Generator 


Motor  Starting  Circuit  (Power) 


Wattmeter  Circuit 


I 


o 
o 

o 


Iron  Cored  Inductance 


196 


MECHANICAL   DRAFTING 


CONVENTIONS    USED    IN    HYDROGRAPH 

ICAL  AND  TOPOGRAPHICAL 

DRAWING. 


Lakes  and  Ponds 


Falls  and  Rapids 


Fresh  and  Salt  Marsh 


APPENDIX 


197 


TOPOGRAPHICAL  CONVENTIONS  (Cont'd) 


Contours 


Depression  Contours 


Cliffs  (Hachured) 


Sand 


198 


MECHANICAL  DRAFTING. 


TOPOGEAPHICAL  CONVENTIONS  (Cont'd) 


&&«& 


Deciduous  Trees  (Oak) 


*    •  *  '  *...„  •  '/•**, 
:;.-".^W 

**-•»<•.,    .*.*..*'•  ^, 

*>>A-^;;V;'; 

.*  •*.•*:.*;::!*, 


Evergreen  Trees 


A.  «•  n, 


Clearing 


Cultivated  Land 


APPENDIX. 
TOPOGEAPHICAL  CONVENTIONS  (Cont'd) 

Hill 


199 


Bridges 


Rail  Fenco 


Hedge 


X X X- 


Buildings  (Large  Scale) 


Buildings  (Small  Scale) 


Traverse  Stations 


Stadia  Stations 


Triangulation  Stations 


B.  M.  x  1143 


o 

Q 


200  MECHANICAL  DRAFTING 

TOPOGRAPHICAL  CONVENTIONS  (Cont'd) 
Canals  and  Ditches 


Double  Track 


Railroads  Two  Lines 


Electric 


In  Road  or  Street 


.Metaled 


Wagon  Roads 


Poor  or  Private 


(Blue) 

Aqueducts  and  Water  Pipes 

(Blue) 

Single  Track.  I    I     I     I     I     I 


Paths  or  Trails  

(Blue) 


APPENDIX 


201 


CONVENTIONAL  REPRESENTATION  OF 
RIVETS. 


SHOP  RIVETS 

FAR 
SIDE 

NEAR 
SIDE 

BOTH 
SIDES 

Two  Full  Heads 

o 

Countersunk  and  Chipped 

® 

g 

K 

Countersunk  and  not  Chipped 

0 

u 

^s 

Flattened  to  1  4  High 

© 

§ 

^ 

Flattened  to  3  8  High 

© 

^ 

% 

FIELD  RIVETS 

Two  Full  Heads 

• 

Countersunk  and  Chipped 

<s> 

® 

38 

STANDARD    RIVET 

H 
*i 

C( 

EADS 

I 

*3L 

L_T 

_N4 

CONE  HEAD 
"*      Q         *" 

/ 

[EAD 

1 

I 

ROUN1 

|— 

~*\  ~* 

DHEAD 

J 

)UNTERSUNK  P 

t  Cf: 

i 

/ 

\ 

V 

^Nj^oo^ 

H^fr  \ 

i 

k 

P 

w 

I     |        " 

r~  r 

202 


MECHANICAL  DRAFTING. 


BEPKESENTATION  OF  EIVETS  (Cont'd) 


14'  4  */-6j  f>b <  pc 
Jfediagrarrtfor  /ocaf/on 


Remainder  of  Bottom  F/anffe  5amt 
a//  f/e/J  ho/fs 
to  6e 
16 ''£'  3L'~  P<2.  Pi 3. 

^T 


APPENDIX. 


203 


SINGLE    LINE    CONVENTIONAL    SYMBOLS 
COMMONLY  USED  IN  MAKING  PRELIM- 
INARY LAY-OUTS,  SMALL  SCALE 
DRAWINGS   AND    SKETCHES 
OF  PIPE  SYSTEMS  WITH 
FITTINGS  AND  AC- 
CESSORIES. 


Hot  Water  Main  (Flow) 


Flanges  (Bolted) 


Tee  and  Ell.  Close  rSame  Plane) 


Tee  and  Ell,  Long  Sweep  (Same  Plane)  Drop  Rise 

I       1  1, 1 


Jranches  taken  from  Bottom  of  Main 


, 

Branches  taken  from  Top  of  Main 


iQi ixi 


Globe  and  Gate  Valve 


=\0\—       \ 

Check  Valve  T| 


01 


Radiator—  Two  Pipe—  Plan 
Return  Main,  Steam  and  Water 


Unions  (Screwed) 


Heat  and  Vent.  Flues,  with  Registers 


204 


MECHANICAL  DRAFTING. 


LAYOUTS  OF  PIPE  SYSTEMS  (Cont'd) 


ej 


Air  Valve  | 

Radiator 

rl«f 

l^f1 

4^ 

V_    Bushing 
Radiator 
Bushing     ^ 

T          0   « 

/                                             \ 

/                         V 

Radiator-one  pipe-Steam 

1 

—  -4 

Drop  and  Air  Valve4 

A 



|                  C 

^*"N 

(f 

1! 
If 

\ 

Cast  Iron  Boiler- 

IJ 

'i 

i 
i 

I 

0  h 

g 

i 

Plan 
7  Sections  -  and  Connections  ~ 

^  Floor  Drain 
Blow  Off  Cock 


APPENDIX. 


205 


WIDELY  USED  SYMBOLS  FOR  REPRESENT- 
ING PIPE  FITTINGS  ON  ELABORATE 
DRAWINGS. 


Tee 


206  MECHANICAL  DRAFTING. 


PIPE  LAYOUT  SHOWN  IN  ISOMETRIC 


APPENDIX. 


207 


SYMBOLS  REPRESENTING  AIR  PIPES  IN 
HEATING  AND  VENTILATING. 


Dampers— Elevation  and  Plan 


\ 


Rectangular.  Ducts 


Deflecting  and  Mixing  Dampers 


Elbows  in  Round  Ducts 


208  MECHANICAL  DRAFTING. 

INFORMATION  FOR  INVENTORS 

Note.  To  those  interested  in  securing  patents  per- 
haps the  best  advice  is  that  they  write  the  Commissioner 
of  Patents  at  Washington,  D.  C.,  for  a  copy  of  the  "  Rules 
of  Practice  in  the  United  States  Patent  Office. ' '  It  may 
be  well,  however,  to  give  here  a  few  suggestions  concern- 
ing the  proper  procedure  in  making  application  for  a 
patent. 

Records  and  Preliminary  Search.  Since  patents  are 
occasionally  contested  on  the  point  of  date  of  conception 
of  the  idea,  it  is  well  to  secure  the  seal  of  a  notary  public 
on  a  drawing,  sketch  or  written  description  of  any  orig- 
inal device  or  improvement  without  delay.  Then  for  a 
fee  of  ten  dollars  a  search  of  the  patent  office  files  will  be 
made  by  any  patent  attorney  and  prints  and  descriptions 
furnished  of  all  similar  devices  on  which  patents  have 
been  granted.  -  In  arranging  for  such  a  preliminary 
search,  the  patent  attorney  should  be  supplied  with  the 
best  possible  sketch  or  drawing  and  description. 

Patent  Application.  If  in  the  opinion  of  the  attor- 
ney consulted  it  seems  possible  to  secure  a  patent  he  will, 
on  instruction,  make  up  the  application  in  the  form  re- 
quired by  the  patent  office  and  containing  the  following : 

(1)  Preamble  stating  the  name  and  residence  of  the 

applicant  and  the  title  of  the  invention. 

(2)  General  statement  of  the  object  and  nature  of 

the  invention. 

(3)  Brief  description  of  the  several  views  of  the 

drawings    (if  the   invention   admits   of  such 
illustration). 


APPENDIX.  "209 

(4)  Detailed  description. 

(5)  Claim  or  claims. 

(6)  Signature  of  inventor. 

(7)  Signature  of  two  witnesses. 

Drawings.  The  drawing  submitted  with  a  patent 
application  must  be  what  is  commonly  termed  a  descrip- 
tive assembly.  A  definite  size  is  specified,  and  in  the 
"Rules  of  Practice"  supplied  by  the  patent  office  are 
given  typical  drawings  and  sheets  of  symbols,  conven- 
tions, etc.,  to  be  followed  by  the  draftsman;  see  accom- 
panying sheets  for  copies  of  these. 


210 


MECHANICAL  DRAFTING. 


TYPICAL  PATENT  OFFICE  DRAWING 


THESIZE  OF  THE  SHEET  MUST  BE  EXACTLY 
10   x  15  INCHES. 


THIS  SPACE  MUST  BE  EIGHT  INCHES' 


APPENDIX. 


211 


PATENT  OFFICE  CONVENTIONS 


COLONS 
rftioiv 


writ  e*<t*<:e 


ABCDEFGHIJKLMNOPQUSTUVIVXYZ 
j&Lm,Ti,op<? 

1234.36  7<39O 


212 


MECHANICAL  DRAFTING. 


PATENT  OFFICE  ELECTRICAL  SYMBOLS 


1    1 


JMTCH 

' 


I 


Wf£  SWITC 

fr 


DOUBLE  POLF 


CHAween 


-wwvw — LMjmr 


-A^VWW 


/WOXCOo 


X7 

.(AOJVfTABlfJ 

Jf 


/9*     C/AClr/r 


. 

i/6HTfi/IM6 
ARRESTER 


£#Ot//V 


PJ. 

ry 

(ore  a  L 


ff 


37- 


jj: 


jg. 


-&- 


rfiUM 

h 


f 


APPENDIX. 


213 


ELECTEICAL  SYMBOLS  (Con't) 


214 


MECHANICAL  DRAFTING. 


METHODS  OF  REPRESENTING 
FACTS  GRAPHICALLY 


APPENDIX.  215 

ALPHABETS. 


ANALPHAB&T 
ARCHITECTS 


rstuvwoa/z  1234567 
Plan  o/jecond  Floor 


A&CDEFtifiUKLM 


AgoM  alphabet  for 

kttennq  plans  &tc. 
c/  / 


216  MECHANICAL  DRAFTING. 

ALPHABETS  (Cont'd) 


ARCHITECTURAL 

LETTEL5—  DETA1L5 


Jmall  •  LetteTtf  •  abcdefg 
hijklmnopcp/tuvwxyz 
Free  andj^ct  Ckozric  in 
effect  emd  feding  dli/*o  . 

A5CDE.FGHI 
JKLMNOPQ, 

LJTUYXWYZ 

Always  «to  be,  ikre,d  in 
JoineLforiii 


APPENDIX. 
ALPHABETS  (Cont'd) 


217 


218 


MECHANICAL  DRAFTING. 
ALPHABETS  (Cont'd) 


APPENDIX. 

GUMMED  LETTERS. 


219 


t 


m  CD  CMCSI 


CUCS} 


220 


MECHANICAL  DRAFTING. 


GUMMED  LETTEES  (Cont'd) 


APPENDIX 


221 


BILL  OF  MATERIAL  (OR  PARTS) 


No.  of 
Pieces 

PatternNo. 

Mark 

Material 

Nome 

1 

A    161 

C.I 

Body 

1 

C   4Z 

" 

Stuffing  Box 

1 

B    74 

" 

Gland 

^ 

M  60 

Brass 

Discs 

i 

D   104 

C.I. 

Hand  Wheel 

i 

5    16 

Brass 

Stem 

i 

L     76 

C.I. 

Gate 

a 

Stud  Bolts 

2 

Hex.  Nuts 

STRAIGHT  WAY  VALVE 

CRANE  COMPANY 

C/-itCAGO,  /L-L-INO/S 

No  v.  ^4,  /9/6                                        Put/Size 

Note:  The  title  and  bi//  of  material  need  not  be 
joined  together. 


INDEX 

[Numbers  Refer  to  Articles] 


Allen   set    screw,    56. 
Alphabet,   Reinhardt,    1. 
Angles,    Co-ordinate,    32. 
Anneal,    69. 
Approximate  mechanical 

method,  in  isometric  projection,  77. 
Architect's  scale,   48. 
Areas,  method  of,  8. 
Arrangement  of  details  in  working  drav 

ing,    41. 
Assembly    drawing,     denned,    uses,    cha 

acteristics,    40. 
Auxiliary  planes   of  projection,    36. 

B. 

Babbitt,  71. 

Ball   pointed  pen,    2. 

Banana   curve,   25. 

Bearings,    71. 

Bevelled  tracing  rule,  46. 

Bill  of  Material,  28. 

Blotters,    22. 

Bolt  terms,    55. 

Bolts,    construction   of,    54. 

Bolts,    dimensioning,    55. 

Bolts   and   nuts,    54. 

Border  lines,    15. 

Bore,  64. 

Boring   machine,    64. 

Bottles,   ink,  use,  etc.,   29. 

Bow    dividers,    adjustment,    etc.,    26. 

Bow    pencil,    use,    care,    etc.,    27. 

Brasses,    71. 

0. 

Carriage   bolts,    54. 
Chamois    roll,    22. 
Characteristic  section  lines,  44. 
Chatter   braces,    62.  ' 
Circles,   in  isometric  projection,   77. 
Circles,  in  oblique  projection,   84 
Circles,  in  perspective,  107. 
Cleaning  pads,  22. 
Cloth,    tracing,    45. 
Compass,   large,  adjustment,  use,   24. 


Compressed  style  of  letters,   3. 

Conventional   lines,    47. 

Conventional  representation  of  threads,  53. 

Co-ordinate   angles,    32. 

Co-ordinate  axes,  in  oblique  projection,  80. 

Co-ordinate  planes,   32. 

Co-ordinate  planes,  in  oblique  projection, 

80. 

Co-ordinate  planes,   revolution   of,    32. 
Co-ordinates,   in  perspective,   105. 
Core,    66. 

Crest,    of    threads,    defined,    52. 
Crowding,  of  letters,  8. 
Curves,    irregular,    25. 
Cylinders,   sectional,  44. 

D. 

Detailed  drawing,  arrangement  of  de- 
tails, 41. 

Detailed   drawing,    denned,    39. 

Detailed   signature,    41. 

Diameter   of    bolts,    55. 

Dies,    58. 

Dimensioning,  in  isometric  projection,  78. 

Dimensioning,   in  oblique  projection,  81. 

Dimensioning,    rules    of,    43. 

Direct   light,    defined,    86. 

Directrices  in  isometric  projection,  73. 

Dividers,   bow,   adjustment,   etc.,  26. 

Dividers,   large,   23. 

Double    threads,    defined,    51. 

Drawing   board,    construction   of,    13. 

Drawing   board,   use,    13. 

Drawing  paper,  position  of  on  board,   14. 

Drawing  paper,  proper  method  of  tack- 
ing, 14. 

Drawing  paper,    quality,    14. 

Drawing    titles,    defined,    10. 

Drill,    63. 

Drill    press,    63. 

Drive   screw,    56. 


Eight   point   method,   in   isometric  projec- 
tion,   77. 


223 


Elements   of   freehand  letters,    3. 
End    plane,    32. 
End    view,     32. 
Engineer's   scale,   48. 
Erasers,   care   of,    21. 
Extended    style    of    letters,    3. 


Fasteners,    49. 

Fillet,    70. 

Finish,    61. 

First  angle,    elimination   of,    32. 

Formation    of   letters,    4. 

Front   view,    32. 

a. 

G.   E.   D.    special   curve,   25. 
Gothic    alphabet,    constructions,    7. 
Guide  for  lettering,  2. 
Guide   lines,    for   lettering,    3. 
Guide  lines,   in  drawing  titles,   11. 
Gummed   letters,    Willson's,    12. 


Harden,    shop    term,    69. 

Helix,  the,   50. 

Hidden    lines,    projections    of,    35. 

Horizon,    in    perspective,    102. 

Horizontal   plane,   32. 


Indirect   light,    defined,    86. 

Ink    bottle,   use,   etc.,   29. 

Inking    of    pens,    proper   method,    2. 

Interpolated   sections.    44. 

Irregular  curves,    25. 

irregular  objects  in  isometric  projection, 

76. 
Irregular    objects,    in    oblique    projection, 

85. 

Irregular  objects,    in   perspective,    108. 
Isometric    axes,    73. 
Isometric    construction,    75. 
Isometric    plane,    72. 
Isometric  propection,  principles  of,   72. 
Isometric  -scale,    74. 


Key   on   flat,    59. 

Keyseat,    59. 

Keys   and   keyways,    59. 


Lag  screws,  56. 

Lead,   of  threads,   defined,    52. 

Length    of    bolts,    55. 

Lettering  pens,   2. 

Letters,  freehand,  formation  of,  4. 

Letters,    gummed,    12. 

Line =O  = Graph,  30. 

Lines,    conventional,    47. 

Lines   of   sight,   in  perspective,   97. 


Machine    holts,    54. 

Machine  sketch,   denned,   88. 

Margins   and  margin  lines,   11. 

Mechanical  engineer's  scale,  48. 

Mechanical    letters,    6. 

Mechanical  spacing,  8. 

Mill,    62. 

Milling  machine,   62. 

Moore's  pen,    2. 


Name  plates,   defined,   9. 

Needle   point,    construction    of,    18. 

Needle   point,    from   Richter   instruments, 

18. 

Normal  style  of  letters,   3. 
Nuts,    54. 

O. 

Oblique    construction,    83. 

Oblique    projection,    defined,    79. 

Oblique    scale,    82. 

Order  of  inking  in  tracing,   45. 

Order  of  pencil  work   on   drawing,   42. 

Order  of  prominence,  in  drawing  title, 
11. 

Order  of  work  on  details,  41. 

Orthographic    projection,    defined,    31. 

Orthographic  projection,  permissible  vio- 
lations of,  84. 

Orthographic  projection,  principles  of, 
32. 

Orthographic  projections,  summary  of 
principles,  33. 

Origin,   in   isometric   projections,    72. 

Ovals,  element  of  freehand  letters,   3. 

P. 

Paper,   drawing,  position  on  board,   14. 
Paper,    drawing,    quality,    14. 


224 


INDEX. 


Paper,    for  lettering,    2. 

Paysan    pen,    2. 

Pen,   ruling,  use,   care,   etc.,   28. 

Pens,   lettering,    2. 

Pencil,    bow,   27. 

Pencil  for  sketching,   91. 

Pencil   work,    order    of,    42. 

Pencils,    numbering,    20. 

Pencils,   sharpening,    20. 

Pencils,   use   of  points,   20. 

Perspective    construction,    106. 

Perspective    drawing,    defined,    96. 

Perspective,  principles  of  construction,  97. 

Picture   plane,    in   perspective,    96. 

Pipe   threads,    57. 

Pitch,    of    threads,    defined,    52. 

Planes,   co-ordinate,   32. 

Planes,  horizontal,  vertical,  end,  32. 

Planes   of  projection,   32. 

Planes  of  projection,   auxiliary,    36. 

Point  of  sight   in  perspective,    99. 

Point  of  sight,  position  of,    109. 

Position   of   object,    in   perspective,    103. 

Positions   of  views   in  working   drawings, 

37. 

Principle  point  in  perspective,  100. 
Principles   of   isometric   projection,    72. 
Principles  of  orthographic  projection,   32. 
Principles   of  shades  and  shadows,    86. 
Profile   plane.    32. 
Projections,    32. 

Projections   of  hidden  lines,    35. 
Projection,    orthographic,    defined,    31. 
Projections   of   objects,    32. 
Projections,    planes    of,    32. 
Prominence,    methods    of   securing,    11. 
Prominence,  order  of,   11. 
Protractor,  use,   etc.,   51. 

R. 

Raised  tracing  rule,   46. 
Ream,    65. 
Reamer,  65 

Reinhardt  alphabet,   1. 
Revolution    of    co-ordinate    planes,    32. 
Root,    of    threads,    defined,    52. 
Round   key,    59. 
Ruling  pen,   use,   care   of,   etc.,   28. 

S. 

Scale,    care  of,    17. 
Scale,  isometric,  74. 
Scale,  use  of,  17. 
Scale    vs.    size,    defined,    48. 


Scales,    defined,    48. 

Scratch  paper,   method  of  spacing,    11. 

Screws,    defined,    56. 

Sectioning,  indication  of  materials,   44. 

Section  lines,  44. 

Sectioning,   principles    of,    44. 

Square    threads,    defined,     51. 

Shade  and  shadow  construction,  87. 

Shade,  defined,  86. 

Shades  and  shadows,   in  isometric  and 

oblique    projection,    86. 
Shadow,   defined,   86. 
Sheppard  lettering  pen,   2. 
Shop   terms,   use,    60. 
Short  cuts,  in  sketching,  94. 
Shoulder   screw,    56. 
Side  view,  32. 
Signature    detail,    41. 
Single   threads,    defined,    51. 
Sketch,    size    of,    92. 
Sketch    stroke,    91. 
Sketching,    procedure,    93. 
Sketching,    short    cuts,    94. 
Slope  guide,  2. 
Spacing,   8. 

Spacing  of  letters  in  titles,    11. 
Spacing,  mechanical,  8. 
Stems,    of   freehand   letters,    3. 
Straight  seated  key,    59. 
Stud  bolt,    54. 

T. 

T-Square,   construction  of,   16. 
T-Square,    proper    use,    16. 
T- Square,   to   clean,    16. 
Tap   drill,    68. 
Tap,    shop    operation,    67. 
Taps,   58. 
Temper,   69. 
Threads,    classified,    51. 
Threads,    conventional    representation    of, 

53. 

Threads,    principles    of,    50. 
Threads,    terms,   52. 
Title,    drawing    construction    of,    11. 
Title,   drawing,    defined,    10. 
Top   view,   32. 
Tracing,    45. 
Tracing    rules,    46. 
Triangles,    to    clean,     19. 
Triangles,    use,    19. 
Tripple  threads,   defined,   51. 
Twist    drills,    63. 


INDEX. 


225 


u. 

Unit  space,   defined,   6. 

V. 

V-threads,  defined,  51. 

Vanishing    point,    in    perspective, 
Vertical    letters,    5. 
Vertical  plane,   32. 


Views,  orthographic,  top,  front,  and  side, 
32. 

W. 

Weights  of  lines,  in  tracing,  45. 
Working  drawings,  defined,  38. 
Working  drawings,  positions  of  views, 

37. 

Wood   screws,    56. 
Woodruff  key,    59. 


INDEX  TO  APPENDIX 

[Numbers  Refer  to  Pages] 


Photographic  Reproductions —  Page 

Blue   printing    162 

Brown    printing    164 

Zinc  etching    169 

Wax  engraving   171 

Half  tones   17?. 

Abbreviations    173 

Refer,  nc    tables 175 

Geometrical    Constructions — 

Ellipse    183 

Parabola   and   hyperbola 187 

Intersections,    tangents 188 


Page 

Conventional   representations    189 

Electrical  symbols   191,  212 

Topographical  conventions 196 

Hydrogaphic  conventions 196 

Rivets     201 

Pipe  conventions 203 

Patent  office  regulations,  etc 208 

Graphic  representation  of  facts 214 

Alphabets     215 

Gummed  letters    219 

Bill  of  Materials.  ..  ...221 


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